[libcxx-commits] [libcxx] 59e56ee - Revert "Reapply "[Clang] Implement resolution for CWG1835 (#92957)" (#98547)"

Haojian Wu via libcxx-commits libcxx-commits at lists.llvm.org
Mon Jul 15 04:22:56 PDT 2024


Author: Haojian Wu
Date: 2024-07-15T13:22:40+02:00
New Revision: 59e56eeb1d9c0d25a522ae09f501a350981a31de

URL: https://github.com/llvm/llvm-project/commit/59e56eeb1d9c0d25a522ae09f501a350981a31de
DIFF: https://github.com/llvm/llvm-project/commit/59e56eeb1d9c0d25a522ae09f501a350981a31de.diff

LOG: Revert "Reapply "[Clang] Implement resolution for CWG1835 (#92957)" (#98547)"

This reverts commit ce4aada6e2135e29839f672a6599db628b53295d and a
follow-up patch 8ef26f1289bf069ccc0d6383f2f4c0116a1206c1.

This new warning can not be fully suppressed by the
`-Wno-missing-dependent-template-keyword` flag, this gives developer no
time to do the cleanup in a large codebase, see https://github.com/llvm/llvm-project/pull/98547#issuecomment-2228250884

Added: 
    

Modified: 
    clang/docs/ReleaseNotes.rst
    clang/include/clang/AST/ExprCXX.h
    clang/include/clang/AST/Stmt.h
    clang/include/clang/AST/UnresolvedSet.h
    clang/include/clang/Basic/DiagnosticParseKinds.td
    clang/include/clang/Parse/Parser.h
    clang/include/clang/Sema/DeclSpec.h
    clang/include/clang/Sema/Lookup.h
    clang/include/clang/Sema/Sema.h
    clang/lib/AST/ASTImporter.cpp
    clang/lib/AST/ExprCXX.cpp
    clang/lib/AST/ItaniumMangle.cpp
    clang/lib/Parse/ParseExpr.cpp
    clang/lib/Parse/ParseExprCXX.cpp
    clang/lib/Sema/SemaCXXScopeSpec.cpp
    clang/lib/Sema/SemaCoroutine.cpp
    clang/lib/Sema/SemaDeclCXX.cpp
    clang/lib/Sema/SemaExpr.cpp
    clang/lib/Sema/SemaExprMember.cpp
    clang/lib/Sema/SemaOverload.cpp
    clang/lib/Sema/SemaStmtAsm.cpp
    clang/lib/Sema/SemaTemplate.cpp
    clang/lib/Sema/SemaTemplateInstantiate.cpp
    clang/lib/Sema/TreeTransform.h
    clang/lib/Serialization/ASTReaderStmt.cpp
    clang/lib/Serialization/ASTWriterStmt.cpp
    clang/test/CXX/basic/basic.lookup/basic.lookup.classref/p1-cxx11.cpp
    clang/test/CXX/basic/basic.lookup/basic.lookup.classref/p1.cpp
    clang/test/CXX/class.derived/class.member.lookup/p8.cpp
    clang/test/CXX/drs/cwg1xx.cpp
    clang/test/CXX/temp/temp.res/p3.cpp
    clang/test/FixIt/fixit.cpp
    clang/test/Misc/warning-flags.c
    clang/test/Parser/cxx2a-concepts-requires-expr.cpp
    clang/test/SemaCXX/cxx0x-noexcept-expression.cpp
    clang/test/SemaCXX/pseudo-destructors.cpp
    clang/test/SemaCXX/static-assert-cxx17.cpp
    clang/test/SemaTemplate/dependent-base-classes.cpp
    clang/test/SemaTemplate/dependent-template-recover.cpp
    clang/test/SemaTemplate/temp_arg_nontype_cxx20.cpp
    clang/test/SemaTemplate/template-id-expr.cpp
    clang/test/SemaTemplate/typename-specifier-3.cpp
    libcxx/include/regex
    llvm/include/llvm/ADT/ArrayRef.h

Removed: 
    clang/test/CXX/basic/basic.lookup/basic.lookup.qual/basic.lookup.qual.general/p3-example3.cpp
    clang/test/CXX/basic/basic.lookup/basic.lookup.qual/basic.lookup.qual.general/p3.cpp
    clang/test/CXX/temp/temp.names/p3-23.cpp


################################################################################
diff  --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 83a1353f3c400..882277efb2114 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -313,10 +313,6 @@ Resolutions to C++ Defect Reports
 - Clang now considers ``noexcept(typeid(expr))`` more carefully, instead of always assuming that ``std::bad_typeid`` can be thrown.
   (`CWG2191: Incorrect result for noexcept(typeid(v)) <https://cplusplus.github.io/CWG/issues/2191.html>`_).
 
-- Clang now correctly implements lookup for the terminal name of a member-qualified nested-name-specifier.
-  (`CWG1835: Dependent member lookup before < <https://cplusplus.github.io/CWG/issues/1835.html>`_).
-  The warning can be disabled via `-Wno-missing-dependent-template-keyword`.
-
 C Language Changes
 ------------------
 

diff  --git a/clang/include/clang/AST/ExprCXX.h b/clang/include/clang/AST/ExprCXX.h
index edaea6fe27cc3..c2feac525c1ea 100644
--- a/clang/include/clang/AST/ExprCXX.h
+++ b/clang/include/clang/AST/ExprCXX.h
@@ -3676,9 +3676,9 @@ class CXXUnresolvedConstructExpr final
 /// an implicit access if a qualifier is provided.
 class CXXDependentScopeMemberExpr final
     : public Expr,
-      private llvm::TrailingObjects<
-          CXXDependentScopeMemberExpr, NestedNameSpecifierLoc, DeclAccessPair,
-          ASTTemplateKWAndArgsInfo, TemplateArgumentLoc> {
+      private llvm::TrailingObjects<CXXDependentScopeMemberExpr,
+                                    ASTTemplateKWAndArgsInfo,
+                                    TemplateArgumentLoc, NamedDecl *> {
   friend class ASTStmtReader;
   friend class ASTStmtWriter;
   friend TrailingObjects;
@@ -3691,15 +3691,17 @@ class CXXDependentScopeMemberExpr final
   /// implicit accesses.
   QualType BaseType;
 
+  /// The nested-name-specifier that precedes the member name, if any.
+  /// FIXME: This could be in principle store as a trailing object.
+  /// However the performance impact of doing so should be investigated first.
+  NestedNameSpecifierLoc QualifierLoc;
+
   /// The member to which this member expression refers, which
   /// can be name, overloaded operator, or destructor.
   ///
   /// FIXME: could also be a template-id
   DeclarationNameInfo MemberNameInfo;
 
-  /// The location of the '->' or '.' operator.
-  SourceLocation OperatorLoc;
-
   // CXXDependentScopeMemberExpr is followed by several trailing objects,
   // some of which optional. They are in order:
   //
@@ -3719,16 +3721,8 @@ class CXXDependentScopeMemberExpr final
     return CXXDependentScopeMemberExprBits.HasTemplateKWAndArgsInfo;
   }
 
-  unsigned getNumUnqualifiedLookups() const {
-    return CXXDependentScopeMemberExprBits.NumUnqualifiedLookups;
-  }
-
-  unsigned numTrailingObjects(OverloadToken<NestedNameSpecifierLoc>) const {
-    return hasQualifier();
-  }
-
-  unsigned numTrailingObjects(OverloadToken<DeclAccessPair>) const {
-    return getNumUnqualifiedLookups();
+  bool hasFirstQualifierFoundInScope() const {
+    return CXXDependentScopeMemberExprBits.HasFirstQualifierFoundInScope;
   }
 
   unsigned numTrailingObjects(OverloadToken<ASTTemplateKWAndArgsInfo>) const {
@@ -3739,32 +3733,33 @@ class CXXDependentScopeMemberExpr final
     return getNumTemplateArgs();
   }
 
+  unsigned numTrailingObjects(OverloadToken<NamedDecl *>) const {
+    return hasFirstQualifierFoundInScope();
+  }
+
   CXXDependentScopeMemberExpr(const ASTContext &Ctx, Expr *Base,
                               QualType BaseType, bool IsArrow,
                               SourceLocation OperatorLoc,
                               NestedNameSpecifierLoc QualifierLoc,
                               SourceLocation TemplateKWLoc,
-                              ArrayRef<DeclAccessPair> UnqualifiedLookups,
+                              NamedDecl *FirstQualifierFoundInScope,
                               DeclarationNameInfo MemberNameInfo,
                               const TemplateArgumentListInfo *TemplateArgs);
 
-  CXXDependentScopeMemberExpr(EmptyShell Empty, bool HasQualifier,
-                              unsigned NumUnqualifiedLookups,
-                              bool HasTemplateKWAndArgsInfo);
+  CXXDependentScopeMemberExpr(EmptyShell Empty, bool HasTemplateKWAndArgsInfo,
+                              bool HasFirstQualifierFoundInScope);
 
 public:
   static CXXDependentScopeMemberExpr *
   Create(const ASTContext &Ctx, Expr *Base, QualType BaseType, bool IsArrow,
          SourceLocation OperatorLoc, NestedNameSpecifierLoc QualifierLoc,
-         SourceLocation TemplateKWLoc,
-         ArrayRef<DeclAccessPair> UnqualifiedLookups,
+         SourceLocation TemplateKWLoc, NamedDecl *FirstQualifierFoundInScope,
          DeclarationNameInfo MemberNameInfo,
          const TemplateArgumentListInfo *TemplateArgs);
 
   static CXXDependentScopeMemberExpr *
-  CreateEmpty(const ASTContext &Ctx, bool HasQualifier,
-              unsigned NumUnqualifiedLookups, bool HasTemplateKWAndArgsInfo,
-              unsigned NumTemplateArgs);
+  CreateEmpty(const ASTContext &Ctx, bool HasTemplateKWAndArgsInfo,
+              unsigned NumTemplateArgs, bool HasFirstQualifierFoundInScope);
 
   /// True if this is an implicit access, i.e. one in which the
   /// member being accessed was not written in the source.  The source
@@ -3789,35 +3784,34 @@ class CXXDependentScopeMemberExpr final
   bool isArrow() const { return CXXDependentScopeMemberExprBits.IsArrow; }
 
   /// Retrieve the location of the '->' or '.' operator.
-  SourceLocation getOperatorLoc() const { return OperatorLoc; }
-
-  /// Determines whether this member expression had a nested-name-specifier
-  /// prior to the name of the member, e.g., x->Base::foo.
-  bool hasQualifier() const {
-    return CXXDependentScopeMemberExprBits.HasQualifier;
-  }
-
-  /// If the member name was qualified, retrieves the nested-name-specifier
-  /// that precedes the member name, with source-location information.
-  NestedNameSpecifierLoc getQualifierLoc() const {
-    if (!hasQualifier())
-      return NestedNameSpecifierLoc();
-    return *getTrailingObjects<NestedNameSpecifierLoc>();
+  SourceLocation getOperatorLoc() const {
+    return CXXDependentScopeMemberExprBits.OperatorLoc;
   }
 
-  /// If the member name was qualified, retrieves the
-  /// nested-name-specifier that precedes the member name. Otherwise, returns
-  /// NULL.
+  /// Retrieve the nested-name-specifier that qualifies the member name.
   NestedNameSpecifier *getQualifier() const {
-    return getQualifierLoc().getNestedNameSpecifier();
+    return QualifierLoc.getNestedNameSpecifier();
   }
 
-  /// Retrieve the declarations found by unqualified lookup for the first
-  /// component name of the nested-name-specifier, if any.
-  ArrayRef<DeclAccessPair> unqualified_lookups() const {
-    if (!getNumUnqualifiedLookups())
-      return std::nullopt;
-    return {getTrailingObjects<DeclAccessPair>(), getNumUnqualifiedLookups()};
+  /// Retrieve the nested-name-specifier that qualifies the member
+  /// name, with source location information.
+  NestedNameSpecifierLoc getQualifierLoc() const { return QualifierLoc; }
+
+  /// Retrieve the first part of the nested-name-specifier that was
+  /// found in the scope of the member access expression when the member access
+  /// was initially parsed.
+  ///
+  /// This function only returns a useful result when member access expression
+  /// uses a qualified member name, e.g., "x.Base::f". Here, the declaration
+  /// returned by this function describes what was found by unqualified name
+  /// lookup for the identifier "Base" within the scope of the member access
+  /// expression itself. At template instantiation time, this information is
+  /// combined with the results of name lookup into the type of the object
+  /// expression itself (the class type of x).
+  NamedDecl *getFirstQualifierFoundInScope() const {
+    if (!hasFirstQualifierFoundInScope())
+      return nullptr;
+    return *getTrailingObjects<NamedDecl *>();
   }
 
   /// Retrieve the name of the member that this expression refers to.

diff  --git a/clang/include/clang/AST/Stmt.h b/clang/include/clang/AST/Stmt.h
index 257a61c97c9c6..9cd7a364cd3f1 100644
--- a/clang/include/clang/AST/Stmt.h
+++ b/clang/include/clang/AST/Stmt.h
@@ -1020,19 +1020,18 @@ class alignas(void *) Stmt {
     LLVM_PREFERRED_TYPE(bool)
     unsigned IsArrow : 1;
 
-    /// True if this member expression used a nested-name-specifier to
-    /// refer to the member, e.g., "x->Base::f".
-    LLVM_PREFERRED_TYPE(bool)
-    unsigned HasQualifier : 1;
-
     /// Whether this member expression has info for explicit template
     /// keyword and arguments.
     LLVM_PREFERRED_TYPE(bool)
     unsigned HasTemplateKWAndArgsInfo : 1;
 
-    /// Number of declarations found by unqualified lookup for the
-    /// first component name of the nested-name-specifier.
-    unsigned NumUnqualifiedLookups;
+    /// See getFirstQualifierFoundInScope() and the comment listing
+    /// the trailing objects.
+    LLVM_PREFERRED_TYPE(bool)
+    unsigned HasFirstQualifierFoundInScope : 1;
+
+    /// The location of the '->' or '.' operator.
+    SourceLocation OperatorLoc;
   };
 
   class OverloadExprBitfields {

diff  --git a/clang/include/clang/AST/UnresolvedSet.h b/clang/include/clang/AST/UnresolvedSet.h
index ef44499ce5926..1369725ab4e96 100644
--- a/clang/include/clang/AST/UnresolvedSet.h
+++ b/clang/include/clang/AST/UnresolvedSet.h
@@ -97,10 +97,6 @@ class UnresolvedSetImpl {
     decls().push_back(DeclAccessPair::make(D, AS));
   }
 
-  void addAllDecls(ArrayRef<DeclAccessPair> Other) {
-    append(iterator(Other.begin()), iterator(Other.end()));
-  }
-
   /// Replaces the given declaration with the new one, once.
   ///
   /// \return true if the set changed

diff  --git a/clang/include/clang/Basic/DiagnosticParseKinds.td b/clang/include/clang/Basic/DiagnosticParseKinds.td
index e00cd47411cb3..12aab09f28556 100644
--- a/clang/include/clang/Basic/DiagnosticParseKinds.td
+++ b/clang/include/clang/Basic/DiagnosticParseKinds.td
@@ -895,9 +895,10 @@ def missing_template_arg_list_after_template_kw : Extension<
   "keyword">, InGroup<DiagGroup<"missing-template-arg-list-after-template-kw">>,
   DefaultError;
 
-def ext_missing_dependent_template_keyword : ExtWarn<
-  "use 'template' keyword to treat '%0' as a dependent template name">,
-  InGroup<DiagGroup<"missing-dependent-template-keyword">>;
+def err_missing_dependent_template_keyword : Error<
+  "use 'template' keyword to treat '%0' as a dependent template name">;
+def warn_missing_dependent_template_keyword : ExtWarn<
+  "use 'template' keyword to treat '%0' as a dependent template name">;
 
 def ext_extern_template : Extension<
   "extern templates are a C++11 extension">, InGroup<CXX11>;

diff  --git a/clang/include/clang/Parse/Parser.h b/clang/include/clang/Parse/Parser.h
index bb3f08aef0378..126fea0aef2a7 100644
--- a/clang/include/clang/Parse/Parser.h
+++ b/clang/include/clang/Parse/Parser.h
@@ -3372,11 +3372,15 @@ class Parser : public CodeCompletionHandler {
   BaseResult ParseBaseSpecifier(Decl *ClassDecl);
   AccessSpecifier getAccessSpecifierIfPresent() const;
 
-  bool ParseUnqualifiedIdTemplateId(
-      CXXScopeSpec &SS, ParsedType ObjectType, bool ObjectHadErrors,
-      SourceLocation TemplateKWLoc, SourceLocation TildeLoc,
-      IdentifierInfo *Name, SourceLocation NameLoc, bool EnteringContext,
-      UnqualifiedId &Id, bool AssumeTemplateId);
+  bool ParseUnqualifiedIdTemplateId(CXXScopeSpec &SS,
+                                    ParsedType ObjectType,
+                                    bool ObjectHadErrors,
+                                    SourceLocation TemplateKWLoc,
+                                    IdentifierInfo *Name,
+                                    SourceLocation NameLoc,
+                                    bool EnteringContext,
+                                    UnqualifiedId &Id,
+                                    bool AssumeTemplateId);
   bool ParseUnqualifiedIdOperator(CXXScopeSpec &SS, bool EnteringContext,
                                   ParsedType ObjectType,
                                   UnqualifiedId &Result);

diff  --git a/clang/include/clang/Sema/DeclSpec.h b/clang/include/clang/Sema/DeclSpec.h
index 9c22c35535ede..425b6e2a0b30c 100644
--- a/clang/include/clang/Sema/DeclSpec.h
+++ b/clang/include/clang/Sema/DeclSpec.h
@@ -75,7 +75,6 @@ class CXXScopeSpec {
   SourceRange Range;
   NestedNameSpecifierLocBuilder Builder;
   ArrayRef<TemplateParameterList *> TemplateParamLists;
-  ArrayRef<DeclAccessPair> UnqualifiedLookups;
 
 public:
   SourceRange getRange() const { return Range; }
@@ -92,13 +91,6 @@ class CXXScopeSpec {
     return TemplateParamLists;
   }
 
-  void setUnqualifiedLookups(ArrayRef<DeclAccessPair> Found) {
-    UnqualifiedLookups = Found;
-  }
-  ArrayRef<DeclAccessPair> getUnqualifiedLookups() const {
-    return UnqualifiedLookups;
-  }
-
   /// Retrieve the representation of the nested-name-specifier.
   NestedNameSpecifier *getScopeRep() const {
     return Builder.getRepresentation();

diff  --git a/clang/include/clang/Sema/Lookup.h b/clang/include/clang/Sema/Lookup.h
index 6b765ef3c980f..b0a08a05ac6a0 100644
--- a/clang/include/clang/Sema/Lookup.h
+++ b/clang/include/clang/Sema/Lookup.h
@@ -483,15 +483,11 @@ class LookupResult {
     ResultKind = Found;
   }
 
-  void addAllDecls(ArrayRef<DeclAccessPair> Other) {
-    Decls.addAllDecls(Other);
-    ResultKind = Found;
-  }
-
   /// Add all the declarations from another set of lookup
   /// results.
   void addAllDecls(const LookupResult &Other) {
-    addAllDecls(Other.Decls.pairs());
+    Decls.append(Other.Decls.begin(), Other.Decls.end());
+    ResultKind = Found;
   }
 
   /// Determine whether no result was found because we could not

diff  --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
index a0821d5298bc4..48dff1b76cc57 100644
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -2803,8 +2803,7 @@ class Sema final : public SemaBase {
   /// (e.g., Base::), perform name lookup for that identifier as a
   /// nested-name-specifier within the given scope, and return the result of
   /// that name lookup.
-  bool LookupFirstQualifierInScope(Scope *S, NestedNameSpecifier *NNS,
-                                   UnresolvedSetImpl &R);
+  NamedDecl *FindFirstQualifierInScope(Scope *S, NestedNameSpecifier *NNS);
 
   /// Keeps information about an identifier in a nested-name-spec.
   ///
@@ -2844,6 +2843,9 @@ class Sema final : public SemaBase {
   /// \param EnteringContext If true, enter the context specified by the
   ///        nested-name-specifier.
   /// \param SS Optional nested name specifier preceding the identifier.
+  /// \param ScopeLookupResult Provides the result of name lookup within the
+  ///        scope of the nested-name-specifier that was computed at template
+  ///        definition time.
   /// \param ErrorRecoveryLookup Specifies if the method is called to improve
   ///        error recovery and what kind of recovery is performed.
   /// \param IsCorrectedToColon If not null, suggestion of replace '::' -> ':'
@@ -2852,6 +2854,11 @@ class Sema final : public SemaBase {
   ///        not '::'.
   /// \param OnlyNamespace If true, only considers namespaces in lookup.
   ///
+  /// This routine 
diff ers only slightly from ActOnCXXNestedNameSpecifier, in
+  /// that it contains an extra parameter \p ScopeLookupResult, which provides
+  /// the result of name lookup within the scope of the nested-name-specifier
+  /// that was computed at template definition time.
+  ///
   /// If ErrorRecoveryLookup is true, then this call is used to improve error
   /// recovery.  This means that it should not emit diagnostics, it should
   /// just return true on failure.  It also means it should only return a valid
@@ -2860,6 +2867,7 @@ class Sema final : public SemaBase {
   /// specifier.
   bool BuildCXXNestedNameSpecifier(Scope *S, NestedNameSpecInfo &IdInfo,
                                    bool EnteringContext, CXXScopeSpec &SS,
+                                   NamedDecl *ScopeLookupResult,
                                    bool ErrorRecoveryLookup,
                                    bool *IsCorrectedToColon = nullptr,
                                    bool OnlyNamespace = false);
@@ -8559,12 +8567,11 @@ class Sema final : public SemaBase {
                           const TemplateArgumentListInfo *TemplateArgs,
                           bool IsDefiniteInstance, const Scope *S);
 
-  ExprResult
-  ActOnDependentMemberExpr(Expr *Base, QualType BaseType, bool IsArrow,
-                           SourceLocation OpLoc, const CXXScopeSpec &SS,
-                           SourceLocation TemplateKWLoc,
-                           const DeclarationNameInfo &NameInfo,
-                           const TemplateArgumentListInfo *TemplateArgs);
+  ExprResult ActOnDependentMemberExpr(
+      Expr *Base, QualType BaseType, bool IsArrow, SourceLocation OpLoc,
+      const CXXScopeSpec &SS, SourceLocation TemplateKWLoc,
+      NamedDecl *FirstQualifierInScope, const DeclarationNameInfo &NameInfo,
+      const TemplateArgumentListInfo *TemplateArgs);
 
   /// The main callback when the parser finds something like
   ///   expression . [nested-name-specifier] identifier
@@ -8620,14 +8627,15 @@ class Sema final : public SemaBase {
   ExprResult BuildMemberReferenceExpr(
       Expr *Base, QualType BaseType, SourceLocation OpLoc, bool IsArrow,
       CXXScopeSpec &SS, SourceLocation TemplateKWLoc,
-      const DeclarationNameInfo &NameInfo,
+      NamedDecl *FirstQualifierInScope, const DeclarationNameInfo &NameInfo,
       const TemplateArgumentListInfo *TemplateArgs, const Scope *S,
       ActOnMemberAccessExtraArgs *ExtraArgs = nullptr);
 
   ExprResult
   BuildMemberReferenceExpr(Expr *Base, QualType BaseType, SourceLocation OpLoc,
                            bool IsArrow, const CXXScopeSpec &SS,
-                           SourceLocation TemplateKWLoc, LookupResult &R,
+                           SourceLocation TemplateKWLoc,
+                           NamedDecl *FirstQualifierInScope, LookupResult &R,
                            const TemplateArgumentListInfo *TemplateArgs,
                            const Scope *S, bool SuppressQualifierCheck = false,
                            ActOnMemberAccessExtraArgs *ExtraArgs = nullptr);
@@ -11115,14 +11123,15 @@ class Sema final : public SemaBase {
                      QualType ObjectType, bool EnteringContext,
                      RequiredTemplateKind RequiredTemplate = SourceLocation(),
                      AssumedTemplateKind *ATK = nullptr,
-                     bool AllowTypoCorrection = true, bool MayBeNNS = false);
+                     bool AllowTypoCorrection = true);
 
-  TemplateNameKind
-  isTemplateName(Scope *S, CXXScopeSpec &SS, bool hasTemplateKeyword,
-                 const UnqualifiedId &Name, ParsedType ObjectType,
-                 bool EnteringContext, TemplateTy &Template,
-                 bool &MemberOfUnknownSpecialization,
-                 bool Disambiguation = false, bool MayBeNNS = false);
+  TemplateNameKind isTemplateName(Scope *S, CXXScopeSpec &SS,
+                                  bool hasTemplateKeyword,
+                                  const UnqualifiedId &Name,
+                                  ParsedType ObjectType, bool EnteringContext,
+                                  TemplateTy &Template,
+                                  bool &MemberOfUnknownSpecialization,
+                                  bool Disambiguation = false);
 
   /// Try to resolve an undeclared template name as a type template.
   ///
@@ -11455,11 +11464,12 @@ class Sema final : public SemaBase {
   /// 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
-  ActOnTemplateName(Scope *S, CXXScopeSpec &SS, SourceLocation TemplateKWLoc,
-                    const UnqualifiedId &Name, ParsedType ObjectType,
-                    bool EnteringContext, TemplateTy &Template,
-                    bool AllowInjectedClassName = false, bool MayBeNNS = false);
+  TemplateNameKind ActOnTemplateName(Scope *S, CXXScopeSpec &SS,
+                                     SourceLocation TemplateKWLoc,
+                                     const UnqualifiedId &Name,
+                                     ParsedType ObjectType,
+                                     bool EnteringContext, TemplateTy &Template,
+                                     bool AllowInjectedClassName = false);
 
   DeclResult ActOnClassTemplateSpecialization(
       Scope *S, unsigned TagSpec, TagUseKind TUK, SourceLocation KWLoc,

diff  --git a/clang/lib/AST/ASTImporter.cpp b/clang/lib/AST/ASTImporter.cpp
index 9bb035c07b8ae..4e1b3a5a94de7 100644
--- a/clang/lib/AST/ASTImporter.cpp
+++ b/clang/lib/AST/ASTImporter.cpp
@@ -8439,14 +8439,8 @@ ExpectedStmt ASTNodeImporter::VisitCXXDependentScopeMemberExpr(
   auto ToOperatorLoc = importChecked(Err, E->getOperatorLoc());
   auto ToQualifierLoc = importChecked(Err, E->getQualifierLoc());
   auto ToTemplateKeywordLoc = importChecked(Err, E->getTemplateKeywordLoc());
-
-  UnresolvedSet<8> ToUnqualifiedLookups;
-  for (auto D : E->unqualified_lookups())
-    if (auto ToDOrErr = import(D.getDecl()))
-      ToUnqualifiedLookups.addDecl(*ToDOrErr);
-    else
-      return ToDOrErr.takeError();
-
+  auto ToFirstQualifierFoundInScope =
+      importChecked(Err, E->getFirstQualifierFoundInScope());
   if (Err)
     return std::move(Err);
 
@@ -8480,7 +8474,7 @@ ExpectedStmt ASTNodeImporter::VisitCXXDependentScopeMemberExpr(
 
   return CXXDependentScopeMemberExpr::Create(
       Importer.getToContext(), ToBase, ToType, E->isArrow(), ToOperatorLoc,
-      ToQualifierLoc, ToTemplateKeywordLoc, ToUnqualifiedLookups.pairs(),
+      ToQualifierLoc, ToTemplateKeywordLoc, ToFirstQualifierFoundInScope,
       ToMemberNameInfo, ResInfo);
 }
 

diff  --git a/clang/lib/AST/ExprCXX.cpp b/clang/lib/AST/ExprCXX.cpp
index 9d2883a8debb7..8d2a1b5611ccc 100644
--- a/clang/lib/AST/ExprCXX.cpp
+++ b/clang/lib/AST/ExprCXX.cpp
@@ -1489,27 +1489,19 @@ SourceLocation CXXUnresolvedConstructExpr::getBeginLoc() const {
 CXXDependentScopeMemberExpr::CXXDependentScopeMemberExpr(
     const ASTContext &Ctx, Expr *Base, QualType BaseType, bool IsArrow,
     SourceLocation OperatorLoc, NestedNameSpecifierLoc QualifierLoc,
-    SourceLocation TemplateKWLoc, ArrayRef<DeclAccessPair> UnqualifiedLookups,
+    SourceLocation TemplateKWLoc, NamedDecl *FirstQualifierFoundInScope,
     DeclarationNameInfo MemberNameInfo,
     const TemplateArgumentListInfo *TemplateArgs)
     : Expr(CXXDependentScopeMemberExprClass, Ctx.DependentTy, VK_LValue,
            OK_Ordinary),
-      Base(Base), BaseType(BaseType), MemberNameInfo(MemberNameInfo),
-      OperatorLoc(OperatorLoc) {
+      Base(Base), BaseType(BaseType), QualifierLoc(QualifierLoc),
+      MemberNameInfo(MemberNameInfo) {
   CXXDependentScopeMemberExprBits.IsArrow = IsArrow;
-  CXXDependentScopeMemberExprBits.HasQualifier = QualifierLoc.hasQualifier();
-  CXXDependentScopeMemberExprBits.NumUnqualifiedLookups =
-      UnqualifiedLookups.size();
   CXXDependentScopeMemberExprBits.HasTemplateKWAndArgsInfo =
       (TemplateArgs != nullptr) || TemplateKWLoc.isValid();
-
-  if (hasQualifier())
-    new (getTrailingObjects<NestedNameSpecifierLoc>())
-        NestedNameSpecifierLoc(QualifierLoc);
-
-  std::uninitialized_copy_n(UnqualifiedLookups.data(),
-                            UnqualifiedLookups.size(),
-                            getTrailingObjects<DeclAccessPair>());
+  CXXDependentScopeMemberExprBits.HasFirstQualifierFoundInScope =
+      FirstQualifierFoundInScope != nullptr;
+  CXXDependentScopeMemberExprBits.OperatorLoc = OperatorLoc;
 
   if (TemplateArgs) {
     auto Deps = TemplateArgumentDependence::None;
@@ -1521,59 +1513,54 @@ CXXDependentScopeMemberExpr::CXXDependentScopeMemberExpr(
         TemplateKWLoc);
   }
 
+  if (hasFirstQualifierFoundInScope())
+    *getTrailingObjects<NamedDecl *>() = FirstQualifierFoundInScope;
   setDependence(computeDependence(this));
 }
 
 CXXDependentScopeMemberExpr::CXXDependentScopeMemberExpr(
-    EmptyShell Empty, bool HasQualifier, unsigned NumUnqualifiedLookups,
-    bool HasTemplateKWAndArgsInfo)
+    EmptyShell Empty, bool HasTemplateKWAndArgsInfo,
+    bool HasFirstQualifierFoundInScope)
     : Expr(CXXDependentScopeMemberExprClass, Empty) {
-  CXXDependentScopeMemberExprBits.HasQualifier = HasQualifier;
-  CXXDependentScopeMemberExprBits.NumUnqualifiedLookups = NumUnqualifiedLookups;
   CXXDependentScopeMemberExprBits.HasTemplateKWAndArgsInfo =
       HasTemplateKWAndArgsInfo;
+  CXXDependentScopeMemberExprBits.HasFirstQualifierFoundInScope =
+      HasFirstQualifierFoundInScope;
 }
 
 CXXDependentScopeMemberExpr *CXXDependentScopeMemberExpr::Create(
     const ASTContext &Ctx, Expr *Base, QualType BaseType, bool IsArrow,
     SourceLocation OperatorLoc, NestedNameSpecifierLoc QualifierLoc,
-    SourceLocation TemplateKWLoc, ArrayRef<DeclAccessPair> UnqualifiedLookups,
+    SourceLocation TemplateKWLoc, NamedDecl *FirstQualifierFoundInScope,
     DeclarationNameInfo MemberNameInfo,
     const TemplateArgumentListInfo *TemplateArgs) {
-  bool HasQualifier = QualifierLoc.hasQualifier();
-  unsigned NumUnqualifiedLookups = UnqualifiedLookups.size();
-  assert(!NumUnqualifiedLookups || HasQualifier);
   bool HasTemplateKWAndArgsInfo =
       (TemplateArgs != nullptr) || TemplateKWLoc.isValid();
   unsigned NumTemplateArgs = TemplateArgs ? TemplateArgs->size() : 0;
-  unsigned Size =
-      totalSizeToAlloc<NestedNameSpecifierLoc, DeclAccessPair,
-                       ASTTemplateKWAndArgsInfo, TemplateArgumentLoc>(
-          HasQualifier, NumUnqualifiedLookups, HasTemplateKWAndArgsInfo,
-          NumTemplateArgs);
+  bool HasFirstQualifierFoundInScope = FirstQualifierFoundInScope != nullptr;
+
+  unsigned Size = totalSizeToAlloc<ASTTemplateKWAndArgsInfo,
+                                   TemplateArgumentLoc, NamedDecl *>(
+      HasTemplateKWAndArgsInfo, NumTemplateArgs, HasFirstQualifierFoundInScope);
 
   void *Mem = Ctx.Allocate(Size, alignof(CXXDependentScopeMemberExpr));
   return new (Mem) CXXDependentScopeMemberExpr(
       Ctx, Base, BaseType, IsArrow, OperatorLoc, QualifierLoc, TemplateKWLoc,
-      UnqualifiedLookups, MemberNameInfo, TemplateArgs);
+      FirstQualifierFoundInScope, MemberNameInfo, TemplateArgs);
 }
 
 CXXDependentScopeMemberExpr *CXXDependentScopeMemberExpr::CreateEmpty(
-    const ASTContext &Ctx, bool HasQualifier, unsigned NumUnqualifiedLookups,
-    bool HasTemplateKWAndArgsInfo, unsigned NumTemplateArgs) {
-  assert(!NumTemplateArgs || HasTemplateKWAndArgsInfo);
-  assert(!NumUnqualifiedLookups || HasQualifier);
+    const ASTContext &Ctx, bool HasTemplateKWAndArgsInfo,
+    unsigned NumTemplateArgs, bool HasFirstQualifierFoundInScope) {
+  assert(NumTemplateArgs == 0 || HasTemplateKWAndArgsInfo);
 
-  unsigned Size =
-      totalSizeToAlloc<NestedNameSpecifierLoc, DeclAccessPair,
-                       ASTTemplateKWAndArgsInfo, TemplateArgumentLoc>(
-          HasQualifier, NumUnqualifiedLookups, HasTemplateKWAndArgsInfo,
-          NumTemplateArgs);
+  unsigned Size = totalSizeToAlloc<ASTTemplateKWAndArgsInfo,
+                                   TemplateArgumentLoc, NamedDecl *>(
+      HasTemplateKWAndArgsInfo, NumTemplateArgs, HasFirstQualifierFoundInScope);
 
   void *Mem = Ctx.Allocate(Size, alignof(CXXDependentScopeMemberExpr));
-  return new (Mem) CXXDependentScopeMemberExpr(EmptyShell(), HasQualifier,
-                                               NumUnqualifiedLookups,
-                                               HasTemplateKWAndArgsInfo);
+  return new (Mem) CXXDependentScopeMemberExpr(
+      EmptyShell(), HasTemplateKWAndArgsInfo, HasFirstQualifierFoundInScope);
 }
 
 CXXThisExpr *CXXThisExpr::Create(const ASTContext &Ctx, SourceLocation L,

diff  --git a/clang/lib/AST/ItaniumMangle.cpp b/clang/lib/AST/ItaniumMangle.cpp
index f14c4762bee6f..5444dcf027fe2 100644
--- a/clang/lib/AST/ItaniumMangle.cpp
+++ b/clang/lib/AST/ItaniumMangle.cpp
@@ -594,10 +594,11 @@ class CXXNameMangler {
   void mangleMemberExprBase(const Expr *base, bool isArrow);
   void mangleMemberExpr(const Expr *base, bool isArrow,
                         NestedNameSpecifier *qualifier,
-                        ArrayRef<DeclAccessPair> UnqualifiedLookups,
+                        NamedDecl *firstQualifierLookup,
                         DeclarationName name,
                         const TemplateArgumentLoc *TemplateArgs,
-                        unsigned NumTemplateArgs, unsigned knownArity);
+                        unsigned NumTemplateArgs,
+                        unsigned knownArity);
   void mangleCastExpression(const Expr *E, StringRef CastEncoding);
   void mangleInitListElements(const InitListExpr *InitList);
   void mangleRequirement(SourceLocation RequiresExprLoc,
@@ -4495,11 +4496,14 @@ void CXXNameMangler::mangleMemberExprBase(const Expr *Base, bool IsArrow) {
 }
 
 /// Mangles a member expression.
-void CXXNameMangler::mangleMemberExpr(
-    const Expr *base, bool isArrow, NestedNameSpecifier *qualifier,
-    ArrayRef<DeclAccessPair> UnqualifiedLookups, DeclarationName member,
-    const TemplateArgumentLoc *TemplateArgs, unsigned NumTemplateArgs,
-    unsigned arity) {
+void CXXNameMangler::mangleMemberExpr(const Expr *base,
+                                      bool isArrow,
+                                      NestedNameSpecifier *qualifier,
+                                      NamedDecl *firstQualifierLookup,
+                                      DeclarationName member,
+                                      const TemplateArgumentLoc *TemplateArgs,
+                                      unsigned NumTemplateArgs,
+                                      unsigned arity) {
   // <expression> ::= dt <expression> <unresolved-name>
   //              ::= pt <expression> <unresolved-name>
   if (base)
@@ -4981,9 +4985,11 @@ void CXXNameMangler::mangleExpression(const Expr *E, unsigned Arity,
   case Expr::MemberExprClass: {
     NotPrimaryExpr();
     const MemberExpr *ME = cast<MemberExpr>(E);
-    mangleMemberExpr(ME->getBase(), ME->isArrow(), ME->getQualifier(),
-                     std::nullopt, ME->getMemberDecl()->getDeclName(),
-                     ME->getTemplateArgs(), ME->getNumTemplateArgs(), Arity);
+    mangleMemberExpr(ME->getBase(), ME->isArrow(),
+                     ME->getQualifier(), nullptr,
+                     ME->getMemberDecl()->getDeclName(),
+                     ME->getTemplateArgs(), ME->getNumTemplateArgs(),
+                     Arity);
     break;
   }
 
@@ -4991,9 +4997,10 @@ void CXXNameMangler::mangleExpression(const Expr *E, unsigned Arity,
     NotPrimaryExpr();
     const UnresolvedMemberExpr *ME = cast<UnresolvedMemberExpr>(E);
     mangleMemberExpr(ME->isImplicitAccess() ? nullptr : ME->getBase(),
-                     ME->isArrow(), ME->getQualifier(), std::nullopt,
-                     ME->getMemberName(), ME->getTemplateArgs(),
-                     ME->getNumTemplateArgs(), Arity);
+                     ME->isArrow(), ME->getQualifier(), nullptr,
+                     ME->getMemberName(),
+                     ME->getTemplateArgs(), ME->getNumTemplateArgs(),
+                     Arity);
     break;
   }
 
@@ -5003,8 +5010,10 @@ void CXXNameMangler::mangleExpression(const Expr *E, unsigned Arity,
       = cast<CXXDependentScopeMemberExpr>(E);
     mangleMemberExpr(ME->isImplicitAccess() ? nullptr : ME->getBase(),
                      ME->isArrow(), ME->getQualifier(),
-                     ME->unqualified_lookups(), ME->getMember(),
-                     ME->getTemplateArgs(), ME->getNumTemplateArgs(), Arity);
+                     ME->getFirstQualifierFoundInScope(),
+                     ME->getMember(),
+                     ME->getTemplateArgs(), ME->getNumTemplateArgs(),
+                     Arity);
     break;
   }
 

diff  --git a/clang/lib/Parse/ParseExpr.cpp b/clang/lib/Parse/ParseExpr.cpp
index 310a38b2cd786..259bfa1d77cdb 100644
--- a/clang/lib/Parse/ParseExpr.cpp
+++ b/clang/lib/Parse/ParseExpr.cpp
@@ -2348,9 +2348,10 @@ Parser::ParsePostfixExpressionSuffix(ExprResult LHS) {
       }
 
       if (!LHS.isInvalid())
-        LHS = Actions.ActOnMemberAccessExpr(
-            getCurScope(), LHS.get(), OpLoc, OpKind, SS, TemplateKWLoc, Name,
-            CurParsedObjCImpl ? CurParsedObjCImpl->Dcl : nullptr);
+        LHS = Actions.ActOnMemberAccessExpr(getCurScope(), LHS.get(), OpLoc,
+                                            OpKind, SS, TemplateKWLoc, Name,
+                                 CurParsedObjCImpl ? CurParsedObjCImpl->Dcl
+                                                   : nullptr);
       if (!LHS.isInvalid()) {
         if (Tok.is(tok::less))
           checkPotentialAngleBracket(LHS);

diff  --git a/clang/lib/Parse/ParseExprCXX.cpp b/clang/lib/Parse/ParseExprCXX.cpp
index 17be090dea3fd..1d364f77a8146 100644
--- a/clang/lib/Parse/ParseExprCXX.cpp
+++ b/clang/lib/Parse/ParseExprCXX.cpp
@@ -100,8 +100,7 @@ void Parser::CheckForTemplateAndDigraph(Token &Next, ParsedType ObjectType,
   bool MemberOfUnknownSpecialization;
   if (!Actions.isTemplateName(getCurScope(), SS, /*hasTemplateKeyword=*/false,
                               TemplateName, ObjectType, EnteringContext,
-                              Template, MemberOfUnknownSpecialization,
-                              /*Disambiguation=*/false, /*MayBeNNS=*/true))
+                              Template, MemberOfUnknownSpecialization))
     return;
 
   FixDigraph(*this, PP, Next, SecondToken, tok::unknown,
@@ -354,8 +353,7 @@ bool Parser::ParseOptionalCXXScopeSpecifier(
       TemplateTy Template;
       TemplateNameKind TNK = Actions.ActOnTemplateName(
           getCurScope(), SS, TemplateKWLoc, TemplateName, ObjectType,
-          EnteringContext, Template, /*AllowInjectedClassName*/ true,
-          /*MayBeNNS=*/true);
+          EnteringContext, Template, /*AllowInjectedClassName*/ true);
       if (AnnotateTemplateIdToken(Template, TNK, SS, TemplateKWLoc,
                                   TemplateName, false))
         return true;
@@ -407,6 +405,7 @@ bool Parser::ParseOptionalCXXScopeSpecifier(
                                       : TemplateId->TemplateNameLoc;
         SS.SetInvalid(SourceRange(StartLoc, CCLoc));
       }
+
       continue;
     }
 
@@ -529,19 +528,18 @@ bool Parser::ParseOptionalCXXScopeSpecifier(
       UnqualifiedId TemplateName;
       TemplateName.setIdentifier(&II, Tok.getLocation());
       bool MemberOfUnknownSpecialization;
-      if (TemplateNameKind TNK = Actions.isTemplateName(
-              getCurScope(), SS,
-              /*hasTemplateKeyword=*/false, TemplateName, ObjectType,
-              EnteringContext, Template, MemberOfUnknownSpecialization,
-              /*Disambiguation=*/false,
-              /*MayBeNNS=*/true)) {
+      if (TemplateNameKind TNK = Actions.isTemplateName(getCurScope(), SS,
+                                              /*hasTemplateKeyword=*/false,
+                                                        TemplateName,
+                                                        ObjectType,
+                                                        EnteringContext,
+                                                        Template,
+                                              MemberOfUnknownSpecialization)) {
         // If lookup didn't find anything, we treat the name as a template-name
         // anyway. C++20 requires this, and in prior language modes it improves
         // error recovery. But before we commit to this, check that we actually
         // have something that looks like a template-argument-list next.
-        if (!IsTypename &&
-            (TNK == TNK_Undeclared_template ||
-             (!HasScopeSpecifier && ObjectType)) &&
+        if (!IsTypename && TNK == TNK_Undeclared_template &&
             isTemplateArgumentList(1) == TPResult::False)
           break;
 
@@ -568,7 +566,11 @@ bool Parser::ParseOptionalCXXScopeSpecifier(
           // member of an unknown specialization. However, this will only
           // parse correctly as a template, so suggest the keyword 'template'
           // before 'getAs' and treat this as a dependent template name.
-          Diag(Tok.getLocation(), diag::ext_missing_dependent_template_keyword)
+          unsigned DiagID = diag::err_missing_dependent_template_keyword;
+          if (getLangOpts().MicrosoftExt)
+            DiagID = diag::warn_missing_dependent_template_keyword;
+
+          Diag(Tok.getLocation(), DiagID)
               << II.getName()
               << FixItHint::CreateInsertion(Tok.getLocation(), "template ");
         }
@@ -1918,12 +1920,12 @@ Parser::ParseCXXPseudoDestructor(Expr *Base, SourceLocation OpLoc,
   // argument list. This affects examples such as
   //   void f(auto *p) { p->~X<int>(); }
   // ... but there's no ambiguity, and nowhere to write 'template' in such an
-  // example, so we accept it anyway
-  if (Tok.is(tok::less) && ParseUnqualifiedIdTemplateId(
-                               SS, ObjectType, Base && Base->containsErrors(),
-                               /*TemplateKWLoc=*/SourceLocation(), TildeLoc,
-                               Name, NameLoc, false, SecondTypeName,
-                               /*AssumeTemplateId=*/true))
+  // example, so we accept it anyway.
+  if (Tok.is(tok::less) &&
+      ParseUnqualifiedIdTemplateId(
+          SS, ObjectType, Base && Base->containsErrors(), SourceLocation(),
+          Name, NameLoc, false, SecondTypeName,
+          /*AssumeTemplateId=*/true))
     return ExprError();
 
   return Actions.ActOnPseudoDestructorExpr(getCurScope(), Base, OpLoc, OpKind,
@@ -2530,9 +2532,8 @@ bool Parser::ParseCXXTypeSpecifierSeq(DeclSpec &DS, DeclaratorContext Context) {
 /// \returns true if a parse error occurred, false otherwise.
 bool Parser::ParseUnqualifiedIdTemplateId(
     CXXScopeSpec &SS, ParsedType ObjectType, bool ObjectHadErrors,
-    SourceLocation TemplateKWLoc, SourceLocation TildeLoc, IdentifierInfo *Name,
-    SourceLocation NameLoc, bool EnteringContext, UnqualifiedId &Id,
-    bool AssumeTemplateId) {
+    SourceLocation TemplateKWLoc, IdentifierInfo *Name, SourceLocation NameLoc,
+    bool EnteringContext, UnqualifiedId &Id, bool AssumeTemplateId) {
   assert(Tok.is(tok::less) && "Expected '<' to finish parsing a template-id");
 
   TemplateTy Template;
@@ -2546,14 +2547,13 @@ bool Parser::ParseUnqualifiedIdTemplateId(
       // this template-id is used to form a nested-name-specifier or not.
       TNK = Actions.ActOnTemplateName(getCurScope(), SS, TemplateKWLoc, Id,
                                       ObjectType, EnteringContext, Template,
-                                      /*AllowInjectedClassName=*/true,
-                                      TildeLoc.isValid());
+                                      /*AllowInjectedClassName*/ true);
     } else {
       bool MemberOfUnknownSpecialization;
-      TNK = Actions.isTemplateName(
-          getCurScope(), SS, TemplateKWLoc.isValid(), Id, ObjectType,
-          EnteringContext, Template, MemberOfUnknownSpecialization,
-          /*Disambiguation=*/false, TildeLoc.isValid());
+      TNK = Actions.isTemplateName(getCurScope(), SS,
+                                   TemplateKWLoc.isValid(), Id,
+                                   ObjectType, EnteringContext, Template,
+                                   MemberOfUnknownSpecialization);
       // If lookup found nothing but we're assuming that this is a template
       // name, double-check that makes sense syntactically before committing
       // to it.
@@ -2580,13 +2580,13 @@ bool Parser::ParseUnqualifiedIdTemplateId(
             else
               Name += Id.Identifier->getName();
           }
-          Diag(Id.StartLocation, diag::ext_missing_dependent_template_keyword)
+          Diag(Id.StartLocation, diag::err_missing_dependent_template_keyword)
               << Name
               << FixItHint::CreateInsertion(Id.StartLocation, "template ");
         }
         TNK = Actions.ActOnTemplateName(
             getCurScope(), SS, TemplateKWLoc, Id, ObjectType, EnteringContext,
-            Template, /*AllowInjectedClassName=*/true, TildeLoc.isValid());
+            Template, /*AllowInjectedClassName*/ true);
       } else if (TNK == TNK_Non_template) {
         return false;
       }
@@ -2611,16 +2611,14 @@ bool Parser::ParseUnqualifiedIdTemplateId(
     bool MemberOfUnknownSpecialization;
     TemplateName.setIdentifier(Name, NameLoc);
     if (ObjectType) {
-      TNK = Actions.ActOnTemplateName(getCurScope(), SS, TemplateKWLoc,
-                                      TemplateName, ObjectType, EnteringContext,
-                                      Template, /*AllowInjectedClassName=*/true,
-                                      /*MayBeNNS=*/true);
+      TNK = Actions.ActOnTemplateName(
+          getCurScope(), SS, TemplateKWLoc, TemplateName, ObjectType,
+          EnteringContext, Template, /*AllowInjectedClassName*/ true);
     } else {
       TNK = Actions.isTemplateName(getCurScope(), SS, TemplateKWLoc.isValid(),
-                                   TemplateName, ObjectType, EnteringContext,
-                                   Template, MemberOfUnknownSpecialization,
-                                   /*Disambiguation=*/false,
-                                   /*MayBeNNS=*/true);
+                                   TemplateName, ObjectType,
+                                   EnteringContext, Template,
+                                   MemberOfUnknownSpecialization);
 
       if (TNK == TNK_Non_template && !Id.DestructorName.get()) {
         Diag(NameLoc, diag::err_destructor_template_id)
@@ -2682,7 +2680,7 @@ bool Parser::ParseUnqualifiedIdTemplateId(
   if (Id.getKind() == UnqualifiedIdKind::IK_ConstructorName)
     Id.setConstructorName(Type.get(), NameLoc, RAngleLoc);
   else
-    Id.setDestructorName(TildeLoc, Type.get(), RAngleLoc);
+    Id.setDestructorName(Id.StartLocation, Type.get(), RAngleLoc);
 
   return false;
 }
@@ -3030,9 +3028,8 @@ bool Parser::ParseUnqualifiedId(CXXScopeSpec &SS, ParsedType ObjectType,
     if (Tok.is(tok::less))
       return ParseUnqualifiedIdTemplateId(
           SS, ObjectType, ObjectHadErrors,
-          TemplateKWLoc ? *TemplateKWLoc : SourceLocation(),
-          /*TildeLoc=*/SourceLocation(), Id, IdLoc, EnteringContext, Result,
-          TemplateSpecified);
+          TemplateKWLoc ? *TemplateKWLoc : SourceLocation(), Id, IdLoc,
+          EnteringContext, Result, TemplateSpecified);
 
     if (TemplateSpecified) {
       TemplateNameKind TNK =
@@ -3127,15 +3124,13 @@ bool Parser::ParseUnqualifiedId(CXXScopeSpec &SS, ParsedType ObjectType,
         Tok.is(tok::less))
       return ParseUnqualifiedIdTemplateId(
           SS, ObjectType, ObjectHadErrors,
-          TemplateKWLoc ? *TemplateKWLoc : SourceLocation(),
-          /*TildeLoc=*/SourceLocation(), /*Name=*/nullptr,
-          /*NameLoc=*/SourceLocation(), EnteringContext, Result,
-          TemplateSpecified);
+          TemplateKWLoc ? *TemplateKWLoc : SourceLocation(), nullptr,
+          SourceLocation(), EnteringContext, Result, TemplateSpecified);
     else if (TemplateSpecified &&
              Actions.ActOnTemplateName(
                  getCurScope(), SS, *TemplateKWLoc, Result, ObjectType,
                  EnteringContext, Template,
-                 /*AllowInjectedClassName=*/true) == TNK_Non_template)
+                 /*AllowInjectedClassName*/ true) == TNK_Non_template)
       return true;
 
     return false;
@@ -3225,8 +3220,8 @@ bool Parser::ParseUnqualifiedId(CXXScopeSpec &SS, ParsedType ObjectType,
       Result.setDestructorName(TildeLoc, nullptr, ClassNameLoc);
       return ParseUnqualifiedIdTemplateId(
           SS, ObjectType, ObjectHadErrors,
-          TemplateKWLoc ? *TemplateKWLoc : SourceLocation(), TildeLoc,
-          ClassName, ClassNameLoc, EnteringContext, Result, TemplateSpecified);
+          TemplateKWLoc ? *TemplateKWLoc : SourceLocation(), ClassName,
+          ClassNameLoc, EnteringContext, Result, TemplateSpecified);
     }
 
     // Note that this is a destructor name.

diff  --git a/clang/lib/Sema/SemaCXXScopeSpec.cpp b/clang/lib/Sema/SemaCXXScopeSpec.cpp
index dd61bb22e3dfa..5b2d65247e72e 100644
--- a/clang/lib/Sema/SemaCXXScopeSpec.cpp
+++ b/clang/lib/Sema/SemaCXXScopeSpec.cpp
@@ -356,41 +356,29 @@ bool Sema::isAcceptableNestedNameSpecifier(const NamedDecl *SD,
   return false;
 }
 
-/// If the given nested-name-specifier begins with a bare identifier
-/// (e.g., Base::), perform name lookup for that identifier as a
-/// nested-name-specifier within the given scope, and return the result of that
-/// name lookup.
-bool Sema::LookupFirstQualifierInScope(Scope *S, NestedNameSpecifier *NNS,
-                                       UnresolvedSetImpl &R) {
-  if (!S)
-    return false;
+NamedDecl *Sema::FindFirstQualifierInScope(Scope *S, NestedNameSpecifier *NNS) {
+  if (!S || !NNS)
+    return nullptr;
 
   while (NNS->getPrefix())
     NNS = NNS->getPrefix();
 
-  // FIXME: This is a rather nasty hack! Ideally we should get the results
-  // from LookupTemplateName/BuildCXXNestedNameSpecifier.
-  const IdentifierInfo *II = NNS->getAsIdentifier();
-  if (!II) {
-    if (const auto *DTST =
-            dyn_cast_if_present<DependentTemplateSpecializationType>(
-                NNS->getAsType()))
-      II = DTST->getIdentifier();
-    else
-      return false;
-  }
-  assert(II && "Missing first qualifier in scope");
-  LookupResult Found(*this, II, SourceLocation(),
-                     NNS->getAsIdentifier() ? LookupNestedNameSpecifierName
-                                            : LookupOrdinaryName);
+  if (NNS->getKind() != NestedNameSpecifier::Identifier)
+    return nullptr;
+
+  LookupResult Found(*this, NNS->getAsIdentifier(), SourceLocation(),
+                     LookupNestedNameSpecifierName);
   LookupName(Found, S);
+  assert(!Found.isAmbiguous() && "Cannot handle ambiguities here yet");
 
-  if (Found.empty())
-    return false;
+  if (!Found.isSingleResult())
+    return nullptr;
 
-  R.addAllDecls(Found.asUnresolvedSet().pairs());
-  Found.suppressDiagnostics();
-  return true;
+  NamedDecl *Result = Found.getFoundDecl();
+  if (isAcceptableNestedNameSpecifier(Result))
+    return Result;
+
+  return nullptr;
 }
 
 namespace {
@@ -419,82 +407,112 @@ class NestedNameSpecifierValidatorCCC final
 
 bool Sema::BuildCXXNestedNameSpecifier(Scope *S, NestedNameSpecInfo &IdInfo,
                                        bool EnteringContext, CXXScopeSpec &SS,
+                                       NamedDecl *ScopeLookupResult,
                                        bool ErrorRecoveryLookup,
                                        bool *IsCorrectedToColon,
                                        bool OnlyNamespace) {
   if (IdInfo.Identifier->isEditorPlaceholder())
     return true;
-  if (IsCorrectedToColon)
-    *IsCorrectedToColon = false;
-
-  QualType ObjectType = GetTypeFromParser(IdInfo.ObjectType);
   LookupResult Found(*this, IdInfo.Identifier, IdInfo.IdentifierLoc,
                      OnlyNamespace ? LookupNamespaceName
                                    : LookupNestedNameSpecifierName);
+  QualType ObjectType = GetTypeFromParser(IdInfo.ObjectType);
 
-  // C++ [basic.lookup.qual.general]p3:
-  //   Qualified name lookup in a class, namespace, or enumeration performs a
-  //   search of the scope associated with it except as specified below.
-  LookupParsedName(Found, S, &SS, ObjectType,
-                   /*AllowBuiltinCreation=*/false, EnteringContext);
-
-  // C++ [basic.lookup.qual.general]p3:
-  //   [...] Unless otherwise specified, a qualified name undergoes qualified
-  //   name lookup in its lookup context from the point where it appears unless
-  //   the lookup context either is dependent and is not the current
-  //   instantiation or is not a class or class template.
-  if (Found.wasNotFoundInCurrentInstantiation()) {
-    // Don't speculate if we're just trying to improve error recovery.
-    if (ErrorRecoveryLookup)
-      return true;
-
-    // The lookup context is dependent and either:
-    // - it is not the current instantiation, or
-    // - it is the current instantiation, it has at least one dependent base
-    //   class, and qualified lookup found nothing.
-    // Build a dependent nested-name-specifier. We will lookup the name again
-    // during instantiation.
-    SS.Extend(Context, IdInfo.Identifier, IdInfo.IdentifierLoc, IdInfo.CCLoc);
-    return false;
+  // Determine where to perform name lookup
+  DeclContext *LookupCtx = nullptr;
+  bool isDependent = false;
+  if (IsCorrectedToColon)
+    *IsCorrectedToColon = false;
+  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");
+    LookupCtx = computeDeclContext(ObjectType);
+    isDependent = ObjectType->isDependentType();
+  } else if (SS.isSet()) {
+    // This nested-name-specifier occurs after another nested-name-specifier,
+    // so look into the context associated with the prior nested-name-specifier.
+    LookupCtx = computeDeclContext(SS, EnteringContext);
+    isDependent = isDependentScopeSpecifier(SS);
+    Found.setContextRange(SS.getRange());
   }
 
   bool ObjectTypeSearchedInScope = false;
+  if (LookupCtx) {
+    // Perform "qualified" name lookup into the declaration context we
+    // computed, which is either the type of the base of a member access
+    // expression or the declaration context associated with a prior
+    // nested-name-specifier.
+
+    // The declaration context must be complete.
+    if (!LookupCtx->isDependentContext() &&
+        RequireCompleteDeclContext(SS, LookupCtx))
+      return true;
 
-  // C++ [basic.lookup.qual.general]p2:
-  //   A member-qualified name is the (unique) component name, if any, of
-  //   - an unqualified-id or
-  //   - a nested-name-specifier of the form type-name :: or namespace-name ::
-  //   in the id-expression of a class member access expression.
-  //
-  // C++ [basic.lookup.qual.general]p3:
-  //   [...] If nothing is found by qualified lookup for a member-qualified
-  //   name that is the terminal name of a nested-name-specifier and is not
-  //   dependent, it undergoes unqualified lookup.
-  //
-  // In 'x.A::B::y', 'A' will undergo unqualified lookup if qualified lookup
-  // in the type of 'x' finds nothing. If the lookup context is dependent,
-  // we perform the unqualified lookup in the template definition context
-  // and store the results so we can replicate the lookup during instantiation.
-  if (Found.empty() && !ObjectType.isNull()) {
-    if (S) {
-      LookupName(Found, S);
-    } else if (!SS.getUnqualifiedLookups().empty()) {
-      Found.addAllDecls(SS.getUnqualifiedLookups());
-      Found.resolveKind();
+    LookupQualifiedName(Found, LookupCtx);
+
+    if (!ObjectType.isNull() && Found.empty()) {
+      // C++ [basic.lookup.classref]p4:
+      //   If the id-expression in a class member access is a qualified-id of
+      //   the form
+      //
+      //        class-name-or-namespace-name::...
+      //
+      //   the class-name-or-namespace-name following the . or -> operator is
+      //   looked up both in the context of the entire postfix-expression and in
+      //   the scope of the class of the object expression. If the name is found
+      //   only in the scope of the class of the object expression, the name
+      //   shall refer to a class-name. If the name is found only in the
+      //   context of the entire postfix-expression, the name shall refer to a
+      //   class-name or namespace-name. [...]
+      //
+      // Qualified name lookup into a class will not find a namespace-name,
+      // so we do not need to diagnose that case specifically. However,
+      // this qualified name lookup may find nothing. In that case, perform
+      // unqualified name lookup in the given scope (if available) or
+      // reconstruct the result from when name lookup was performed at template
+      // definition time.
+      if (S)
+        LookupName(Found, S);
+      else if (ScopeLookupResult)
+        Found.addDecl(ScopeLookupResult);
+
+      ObjectTypeSearchedInScope = true;
     }
-    ObjectTypeSearchedInScope = true;
+  } else if (!isDependent) {
+    // Perform unqualified name lookup in the current scope.
+    LookupName(Found, S);
   }
 
   if (Found.isAmbiguous())
     return true;
 
+  // If we performed lookup into a dependent context and did not find anything,
+  // that's fine: just build a dependent nested-name-specifier.
+  if (Found.empty() && isDependent &&
+      !(LookupCtx && LookupCtx->isRecord() &&
+        (!cast<CXXRecordDecl>(LookupCtx)->hasDefinition() ||
+         !cast<CXXRecordDecl>(LookupCtx)->hasAnyDependentBases()))) {
+    // Don't speculate if we're just trying to improve error recovery.
+    if (ErrorRecoveryLookup)
+      return true;
+
+    // We were not able to compute the declaration context for a dependent
+    // base object type or prior nested-name-specifier, so this
+    // nested-name-specifier refers to an unknown specialization. Just build
+    // a dependent nested-name-specifier.
+    SS.Extend(Context, IdInfo.Identifier, IdInfo.IdentifierLoc, IdInfo.CCLoc);
+    return false;
+  }
+
   if (Found.empty() && !ErrorRecoveryLookup) {
     // If identifier is not found as class-name-or-namespace-name, but is found
     // as other entity, don't look for typos.
     LookupResult R(*this, Found.getLookupNameInfo(), LookupOrdinaryName);
-    LookupParsedName(R, S, &SS, ObjectType,
-                     /*AllowBuiltinCreation=*/false, EnteringContext);
-
+    if (LookupCtx)
+      LookupQualifiedName(R, LookupCtx);
+    else if (S && !isDependent)
+      LookupName(R, S);
     if (!R.empty()) {
       // Don't diagnose problems with this speculative lookup.
       R.suppressDiagnostics();
@@ -521,11 +539,6 @@ bool Sema::BuildCXXNestedNameSpecifier(Scope *S, NestedNameSpecInfo &IdInfo,
     }
   }
 
-  DeclContext *LookupCtx =
-      SS.isSet()
-          ? computeDeclContext(SS, EnteringContext)
-          : (!ObjectType.isNull() ? computeDeclContext(ObjectType) : nullptr);
-
   if (Found.empty() && !ErrorRecoveryLookup && !getLangOpts().MSVCCompat) {
     // We haven't found anything, and we're not recovering from a
     // 
diff erent kind of error, so look for typos.
@@ -581,14 +594,14 @@ bool Sema::BuildCXXNestedNameSpecifier(Scope *S, NestedNameSpecInfo &IdInfo,
       // scope, reconstruct the result from the template instantiation itself.
       //
       // Note that C++11 does *not* perform this redundant lookup.
-      NamedDecl *OuterDecl = nullptr;
+      NamedDecl *OuterDecl;
       if (S) {
         LookupResult FoundOuter(*this, IdInfo.Identifier, IdInfo.IdentifierLoc,
                                 LookupNestedNameSpecifierName);
         LookupName(FoundOuter, S);
         OuterDecl = FoundOuter.getAsSingle<NamedDecl>();
-      } else if (!SS.getUnqualifiedLookups().empty())
-        OuterDecl = SS.getUnqualifiedLookups().front().getDecl();
+      } else
+        OuterDecl = ScopeLookupResult;
 
       if (isAcceptableNestedNameSpecifier(OuterDecl) &&
           OuterDecl->getCanonicalDecl() != SD->getCanonicalDecl() &&
@@ -766,7 +779,7 @@ bool Sema::ActOnCXXNestedNameSpecifier(Scope *S, NestedNameSpecInfo &IdInfo,
     return true;
 
   return BuildCXXNestedNameSpecifier(S, IdInfo, EnteringContext, SS,
-                                     /*ErrorRecoveryLookup=*/false,
+                                     /*ScopeLookupResult=*/nullptr, false,
                                      IsCorrectedToColon, OnlyNamespace);
 }
 
@@ -827,7 +840,7 @@ bool Sema::IsInvalidUnlessNestedName(Scope *S, CXXScopeSpec &SS,
     return false;
 
   return !BuildCXXNestedNameSpecifier(S, IdInfo, EnteringContext, SS,
-                                      /*ErrorRecoveryLookup=*/true);
+                                      /*ScopeLookupResult=*/nullptr, true);
 }
 
 bool Sema::ActOnCXXNestedNameSpecifier(Scope *S,

diff  --git a/clang/lib/Sema/SemaCoroutine.cpp b/clang/lib/Sema/SemaCoroutine.cpp
index fa0eb1d2afbee..81334c817b2af 100644
--- a/clang/lib/Sema/SemaCoroutine.cpp
+++ b/clang/lib/Sema/SemaCoroutine.cpp
@@ -306,8 +306,8 @@ static ExprResult buildMemberCall(Sema &S, Expr *Base, SourceLocation Loc,
   // FIXME: Fix BuildMemberReferenceExpr to take a const CXXScopeSpec&.
   CXXScopeSpec SS;
   ExprResult Result = S.BuildMemberReferenceExpr(
-      Base, Base->getType(), Loc, /*IsPtr=*/false, SS, SourceLocation(),
-      NameInfo, /*TemplateArgs=*/nullptr,
+      Base, Base->getType(), Loc, /*IsPtr=*/false, SS,
+      SourceLocation(), nullptr, NameInfo, /*TemplateArgs=*/nullptr,
       /*Scope=*/nullptr);
   if (Result.isInvalid())
     return ExprError();

diff  --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 76db539b5726b..17c4ba99c03f5 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -1275,11 +1275,9 @@ static bool checkTupleLikeDecomposition(Sema &S,
     if (UseMemberGet) {
       //   if [lookup of member get] finds at least one declaration, the
       //   initializer is e.get<i-1>().
-      E = S.BuildMemberReferenceExpr(E.get(), DecompType, Loc,
-                                     /*IsArrow=*/false,
-                                     /*SS=*/CXXScopeSpec(),
-                                     /*TemplateKWLoc=*/SourceLocation(),
-                                     MemberGet, &Args, /*S=*/nullptr);
+      E = S.BuildMemberReferenceExpr(E.get(), DecompType, Loc, false,
+                                     CXXScopeSpec(), SourceLocation(), nullptr,
+                                     MemberGet, &Args, nullptr);
       if (E.isInvalid())
         return true;
 
@@ -4903,12 +4901,16 @@ BuildImplicitMemberInitializer(Sema &SemaRef, CXXConstructorDecl *Constructor,
     MemberLookup.addDecl(Indirect ? cast<ValueDecl>(Indirect)
                                   : cast<ValueDecl>(Field), AS_public);
     MemberLookup.resolveKind();
-    ExprResult CtorArg = SemaRef.BuildMemberReferenceExpr(
-        MemberExprBase, ParamType, Loc,
-        /*IsArrow=*/false, SS,
-        /*TemplateKWLoc=*/SourceLocation(), MemberLookup,
-        /*TemplateArgs=*/nullptr,
-        /*S=*/nullptr);
+    ExprResult CtorArg
+      = SemaRef.BuildMemberReferenceExpr(MemberExprBase,
+                                         ParamType, Loc,
+                                         /*IsArrow=*/false,
+                                         SS,
+                                         /*TemplateKWLoc=*/SourceLocation(),
+                                         /*FirstQualifierInScope=*/nullptr,
+                                         MemberLookup,
+                                         /*TemplateArgs=*/nullptr,
+                                         /*S*/nullptr);
     if (CtorArg.isInvalid())
       return true;
 
@@ -14337,10 +14339,8 @@ class MemberBuilder: public ExprBuilder {
 public:
   Expr *build(Sema &S, SourceLocation Loc) const override {
     return assertNotNull(S.BuildMemberReferenceExpr(
-                              Builder.build(S, Loc), Type, Loc, IsArrow, SS,
-                              /*TemplateKwLoc=*/SourceLocation(), MemberLookup,
-                              /*TemplateArgs=*/nullptr, /*S=*/nullptr)
-                             .get());
+        Builder.build(S, Loc), Type, Loc, IsArrow, SS, SourceLocation(),
+        nullptr, MemberLookup, nullptr, nullptr).get());
   }
 
   MemberBuilder(const ExprBuilder &Builder, QualType Type, bool IsArrow,
@@ -14546,11 +14546,13 @@ buildSingleCopyAssignRecursively(Sema &S, SourceLocation Loc, QualType T,
                    Loc);
 
     // Create the reference to operator=.
-    ExprResult OpEqualRef = S.BuildMemberReferenceExpr(
-        To.build(S, Loc), T, Loc, /*IsArrow=*/false, SS,
-        /*TemplateKWLoc=*/SourceLocation(), OpLookup,
-        /*TemplateArgs=*/nullptr, /*S*/ nullptr,
-        /*SuppressQualifierCheck=*/true);
+    ExprResult OpEqualRef
+      = S.BuildMemberReferenceExpr(To.build(S, Loc), T, Loc, /*IsArrow=*/false,
+                                   SS, /*TemplateKWLoc=*/SourceLocation(),
+                                   /*FirstQualifierInScope=*/nullptr,
+                                   OpLookup,
+                                   /*TemplateArgs=*/nullptr, /*S*/nullptr,
+                                   /*SuppressQualifierCheck=*/true);
     if (OpEqualRef.isInvalid())
       return StmtError();
 
@@ -17156,9 +17158,8 @@ bool Sema::EvaluateStaticAssertMessageAsString(Expr *Message,
 
   auto BuildExpr = [&](LookupResult &LR) {
     ExprResult Res = BuildMemberReferenceExpr(
-        Message, Message->getType(), Message->getBeginLoc(), /*IsArrow=*/false,
-        /*SS=*/CXXScopeSpec(), /*TemplateKWLoc=*/SourceLocation(), LR,
-        /*TemplateArgs=*/nullptr, /*S=*/nullptr);
+        Message, Message->getType(), Message->getBeginLoc(), false,
+        CXXScopeSpec(), SourceLocation(), nullptr, LR, nullptr, nullptr);
     if (Res.isInvalid())
       return ExprError();
     Res = BuildCallExpr(nullptr, Res.get(), Loc, std::nullopt, Loc, nullptr,

diff  --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 9940f8cb62955..d6b85cbcaf56b 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -2624,7 +2624,7 @@ recoverFromMSUnqualifiedLookup(Sema &S, ASTContext &Context,
     return CXXDependentScopeMemberExpr::Create(
         Context, /*This=*/nullptr, ThisType, /*IsArrow=*/true,
         /*Op=*/SourceLocation(), NestedNameSpecifierLoc(), TemplateKWLoc,
-        /*UnqualifiedLookups=*/std::nullopt, NameInfo, TemplateArgs);
+        /*FirstQualifierFoundInScope=*/nullptr, NameInfo, TemplateArgs);
   }
 
   // Synthesize a fake NNS that points to the derived class.  This will

diff  --git a/clang/lib/Sema/SemaExprMember.cpp b/clang/lib/Sema/SemaExprMember.cpp
index 8519618bacfee..2070f3b7bb3a2 100644
--- a/clang/lib/Sema/SemaExprMember.cpp
+++ b/clang/lib/Sema/SemaExprMember.cpp
@@ -552,9 +552,11 @@ static Decl *FindGetterSetterNameDecl(const ObjCObjectPointerType *QIdTy,
 }
 
 ExprResult
-Sema::ActOnDependentMemberExpr(Expr *BaseExpr, QualType BaseType, bool IsArrow,
-                               SourceLocation OpLoc, const CXXScopeSpec &SS,
+Sema::ActOnDependentMemberExpr(Expr *BaseExpr, QualType BaseType,
+                               bool IsArrow, SourceLocation OpLoc,
+                               const CXXScopeSpec &SS,
                                SourceLocation TemplateKWLoc,
+                               NamedDecl *FirstQualifierInScope,
                                const DeclarationNameInfo &NameInfo,
                                const TemplateArgumentListInfo *TemplateArgs) {
   // Even in dependent contexts, try to diagnose base expressions with
@@ -588,8 +590,8 @@ Sema::ActOnDependentMemberExpr(Expr *BaseExpr, QualType BaseType, bool IsArrow,
   // must have pointer type, and the accessed type is the pointee.
   return CXXDependentScopeMemberExpr::Create(
       Context, BaseExpr, BaseType, IsArrow, OpLoc,
-      SS.getWithLocInContext(Context), TemplateKWLoc,
-      SS.getUnqualifiedLookups(), NameInfo, TemplateArgs);
+      SS.getWithLocInContext(Context), TemplateKWLoc, FirstQualifierInScope,
+      NameInfo, TemplateArgs);
 }
 
 /// We know that the given qualified member reference points only to
@@ -765,9 +767,8 @@ static bool LookupMemberExprInRecord(Sema &SemaRef, LookupResult &R,
           R.addDecl(ND);
         R.resolveKind();
         return SemaRef.BuildMemberReferenceExpr(
-            BaseExpr, BaseExpr->getType(), OpLoc, IsArrow, SS,
-            /*TemplateKWLoc=*/SourceLocation(), R, /*TemplateArgs=*/nullptr,
-            /*S=*/nullptr);
+            BaseExpr, BaseExpr->getType(), OpLoc, IsArrow, SS, SourceLocation(),
+            nullptr, R, nullptr, nullptr);
       },
       Sema::CTK_ErrorRecovery, DC);
 
@@ -783,7 +784,7 @@ static ExprResult LookupMemberExpr(Sema &S, LookupResult &R,
 ExprResult Sema::BuildMemberReferenceExpr(
     Expr *Base, QualType BaseType, SourceLocation OpLoc, bool IsArrow,
     CXXScopeSpec &SS, SourceLocation TemplateKWLoc,
-    const DeclarationNameInfo &NameInfo,
+    NamedDecl *FirstQualifierInScope, const DeclarationNameInfo &NameInfo,
     const TemplateArgumentListInfo *TemplateArgs, const Scope *S,
     ActOnMemberAccessExtraArgs *ExtraArgs) {
   LookupResult R(*this, NameInfo, LookupMemberName);
@@ -827,9 +828,10 @@ ExprResult Sema::BuildMemberReferenceExpr(
   if (SS.isInvalid())
     return ExprError();
 
-  return BuildMemberReferenceExpr(Base, BaseType, OpLoc, IsArrow, SS,
-                                  TemplateKWLoc, R, TemplateArgs, S,
-                                  /*SuppressQualifierCheck=*/false, ExtraArgs);
+  return BuildMemberReferenceExpr(Base, BaseType,
+                                  OpLoc, IsArrow, SS, TemplateKWLoc,
+                                  FirstQualifierInScope, R, TemplateArgs, S,
+                                  false, ExtraArgs);
 }
 
 ExprResult
@@ -967,11 +969,17 @@ static bool IsInFnTryBlockHandler(const Scope *S) {
   return false;
 }
 
-ExprResult Sema::BuildMemberReferenceExpr(
-    Expr *BaseExpr, QualType BaseExprType, SourceLocation OpLoc, bool IsArrow,
-    const CXXScopeSpec &SS, SourceLocation TemplateKWLoc, LookupResult &R,
-    const TemplateArgumentListInfo *TemplateArgs, const Scope *S,
-    bool SuppressQualifierCheck, ActOnMemberAccessExtraArgs *ExtraArgs) {
+ExprResult
+Sema::BuildMemberReferenceExpr(Expr *BaseExpr, QualType BaseExprType,
+                               SourceLocation OpLoc, bool IsArrow,
+                               const CXXScopeSpec &SS,
+                               SourceLocation TemplateKWLoc,
+                               NamedDecl *FirstQualifierInScope,
+                               LookupResult &R,
+                               const TemplateArgumentListInfo *TemplateArgs,
+                               const Scope *S,
+                               bool SuppressQualifierCheck,
+                               ActOnMemberAccessExtraArgs *ExtraArgs) {
   assert(!SS.isInvalid() && "nested-name-specifier cannot be invalid");
   // If the member wasn't found in the current instantiation, or if the
   // arrow operator was used with a dependent non-pointer object expression,
@@ -981,8 +989,8 @@ ExprResult Sema::BuildMemberReferenceExpr(
        (SS.isSet() ? SS.getScopeRep()->isDependent()
                    : BaseExprType->isDependentType())))
     return ActOnDependentMemberExpr(BaseExpr, BaseExprType, IsArrow, OpLoc, SS,
-                                    TemplateKWLoc, R.getLookupNameInfo(),
-                                    TemplateArgs);
+                                    TemplateKWLoc, FirstQualifierInScope,
+                                    R.getLookupNameInfo(), TemplateArgs);
 
   QualType BaseType = BaseExprType;
   if (IsArrow) {
@@ -1187,9 +1195,9 @@ ExprResult Sema::BuildMemberReferenceExpr(
 
     // Non-dependent member, but dependent template arguments.
     if (!VDecl.get())
-      return ActOnDependentMemberExpr(BaseExpr, BaseExpr->getType(), IsArrow,
-                                      OpLoc, SS, TemplateKWLoc, MemberNameInfo,
-                                      TemplateArgs);
+      return ActOnDependentMemberExpr(
+          BaseExpr, BaseExpr->getType(), IsArrow, OpLoc, SS, TemplateKWLoc,
+          FirstQualifierInScope, MemberNameInfo, TemplateArgs);
 
     VarDecl *Var = cast<VarDecl>(VDecl.get());
     if (!Var->getTemplateSpecializationKind())
@@ -1755,16 +1763,15 @@ ExprResult Sema::ActOnMemberAccessExpr(Scope *S, Expr *Base,
   const TemplateArgumentListInfo *TemplateArgs;
   DecomposeUnqualifiedId(Id, TemplateArgsBuffer,
                          NameInfo, TemplateArgs);
-  bool IsArrow = OpKind == tok::arrow;
+
+  bool IsArrow = (OpKind == tok::arrow);
 
   if (getLangOpts().HLSL && IsArrow)
     return ExprError(Diag(OpLoc, diag::err_hlsl_operator_unsupported) << 2);
 
-  UnresolvedSet<4> UnqualifiedLookups;
-  if (SS.isValid() &&
-      LookupFirstQualifierInScope(S, SS.getScopeRep(), UnqualifiedLookups)) {
-    SS.setUnqualifiedLookups(UnqualifiedLookups.pairs());
-  }
+  NamedDecl *FirstQualifierInScope
+    = (!SS.isSet() ? nullptr : FindFirstQualifierInScope(S, SS.getScopeRep()));
+
   // This is a postfix expression, so get rid of ParenListExprs.
   ExprResult Result = MaybeConvertParenListExprToParenExpr(S, Base);
   if (Result.isInvalid()) return ExprError();
@@ -1772,8 +1779,8 @@ ExprResult Sema::ActOnMemberAccessExpr(Scope *S, Expr *Base,
 
   ActOnMemberAccessExtraArgs ExtraArgs = {S, Id, ObjCImpDecl};
   ExprResult Res = BuildMemberReferenceExpr(
-      Base, Base->getType(), OpLoc, IsArrow, SS, TemplateKWLoc, NameInfo,
-      TemplateArgs, S, &ExtraArgs);
+      Base, Base->getType(), OpLoc, IsArrow, SS, TemplateKWLoc,
+      FirstQualifierInScope, NameInfo, TemplateArgs, S, &ExtraArgs);
 
   if (!Res.isInvalid() && isa<MemberExpr>(Res.get()))
     CheckMemberAccessOfNoDeref(cast<MemberExpr>(Res.get()));
@@ -1917,8 +1924,9 @@ Sema::BuildImplicitMemberExpr(const CXXScopeSpec &SS,
     baseExpr = BuildCXXThisExpr(loc, ThisTy, /*IsImplicit=*/true);
   }
 
-  return BuildMemberReferenceExpr(baseExpr, ThisTy,
-                                  /*OpLoc=*/SourceLocation(),
-                                  /*IsArrow=*/!getLangOpts().HLSL, SS,
-                                  TemplateKWLoc, R, TemplateArgs, S);
+  return BuildMemberReferenceExpr(
+      baseExpr, ThisTy,
+      /*OpLoc=*/SourceLocation(),
+      /*IsArrow=*/!getLangOpts().HLSL, SS, TemplateKWLoc,
+      /*FirstQualifierInScope=*/nullptr, R, TemplateArgs, S);
 }

diff  --git a/clang/lib/Sema/SemaOverload.cpp b/clang/lib/Sema/SemaOverload.cpp
index d4a48858ec419..074062ebbb594 100644
--- a/clang/lib/Sema/SemaOverload.cpp
+++ b/clang/lib/Sema/SemaOverload.cpp
@@ -16036,11 +16036,13 @@ Sema::BuildForRangeBeginEndCall(SourceLocation Loc,
 
   CandidateSet->clear(OverloadCandidateSet::CSK_Normal);
   if (!MemberLookup.empty()) {
-    ExprResult MemberRef = BuildMemberReferenceExpr(
-        Range, Range->getType(), Loc,
-        /*IsPtr=*/false, /*SS=*/CXXScopeSpec(),
-        /*TemplateKWLoc=*/SourceLocation(), MemberLookup,
-        /*TemplateArgs=*/nullptr, S);
+    ExprResult MemberRef =
+        BuildMemberReferenceExpr(Range, Range->getType(), Loc,
+                                 /*IsPtr=*/false, CXXScopeSpec(),
+                                 /*TemplateKWLoc=*/SourceLocation(),
+                                 /*FirstQualifierInScope=*/nullptr,
+                                 MemberLookup,
+                                 /*TemplateArgs=*/nullptr, S);
     if (MemberRef.isInvalid()) {
       *CallExpr = ExprError();
       return FRS_DiagnosticIssued;

diff  --git a/clang/lib/Sema/SemaStmtAsm.cpp b/clang/lib/Sema/SemaStmtAsm.cpp
index da2e99b6bc00c..32d42f3c3f3bb 100644
--- a/clang/lib/Sema/SemaStmtAsm.cpp
+++ b/clang/lib/Sema/SemaStmtAsm.cpp
@@ -900,8 +900,7 @@ Sema::LookupInlineAsmVarDeclField(Expr *E, StringRef Member,
     return CXXDependentScopeMemberExpr::Create(
         Context, E, T, /*IsArrow=*/false, AsmLoc, NestedNameSpecifierLoc(),
         SourceLocation(),
-        /*UnqualifiedLookups=*/std::nullopt, NameInfo,
-        /*TemplateArgs=*/nullptr);
+        /*FirstQualifierFoundInScope=*/nullptr, NameInfo, /*TemplateArgs=*/nullptr);
   }
 
   const RecordType *RT = T->getAs<RecordType>();
@@ -924,9 +923,8 @@ Sema::LookupInlineAsmVarDeclField(Expr *E, StringRef Member,
 
   // Make an Expr to thread through OpDecl.
   ExprResult Result = BuildMemberReferenceExpr(
-      E, E->getType(), AsmLoc, /*IsArrow=*/false, /*SS=*/CXXScopeSpec(),
-      /*TemplateKWLoc*/ SourceLocation(), FieldResult,
-      /*TemplateArgs=*/nullptr, /*S=*/nullptr);
+      E, E->getType(), AsmLoc, /*IsArrow=*/false, CXXScopeSpec(),
+      SourceLocation(), nullptr, FieldResult, nullptr, nullptr);
 
   return Result;
 }

diff  --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index d80e50deef697..9d96201625389 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -174,12 +174,15 @@ bool Sema::hasAnyAcceptableTemplateNames(LookupResult &R,
   return false;
 }
 
-TemplateNameKind
-Sema::isTemplateName(Scope *S, CXXScopeSpec &SS, bool hasTemplateKeyword,
-                     const UnqualifiedId &Name, ParsedType ObjectTypePtr,
-                     bool EnteringContext, TemplateTy &TemplateResult,
-                     bool &MemberOfUnknownSpecialization, bool Disambiguation,
-                     bool MayBeNNS) {
+TemplateNameKind Sema::isTemplateName(Scope *S,
+                                      CXXScopeSpec &SS,
+                                      bool hasTemplateKeyword,
+                                      const UnqualifiedId &Name,
+                                      ParsedType ObjectTypePtr,
+                                      bool EnteringContext,
+                                      TemplateTy &TemplateResult,
+                                      bool &MemberOfUnknownSpecialization,
+                                      bool Disambiguation) {
   assert(getLangOpts().CPlusPlus && "No template names in C!");
 
   DeclarationName TName;
@@ -210,9 +213,8 @@ Sema::isTemplateName(Scope *S, CXXScopeSpec &SS, bool hasTemplateKeyword,
   if (LookupTemplateName(R, S, SS, ObjectType, EnteringContext,
                          /*RequiredTemplate=*/SourceLocation(),
                          &AssumedTemplate,
-                         /*AllowTypoCorrection=*/!Disambiguation, MayBeNNS))
+                         /*AllowTypoCorrection=*/!Disambiguation))
     return TNK_Non_template;
-
   MemberOfUnknownSpecialization = R.wasNotFoundInCurrentInstantiation();
 
   if (AssumedTemplate != AssumedTemplateKind::None) {
@@ -378,7 +380,7 @@ bool Sema::LookupTemplateName(LookupResult &Found, Scope *S, CXXScopeSpec &SS,
                               QualType ObjectType, bool EnteringContext,
                               RequiredTemplateKind RequiredTemplate,
                               AssumedTemplateKind *ATK,
-                              bool AllowTypoCorrection, bool MayBeNNS) {
+                              bool AllowTypoCorrection) {
   if (ATK)
     *ATK = AssumedTemplateKind::None;
 
@@ -387,89 +389,92 @@ bool Sema::LookupTemplateName(LookupResult &Found, Scope *S, CXXScopeSpec &SS,
 
   Found.setTemplateNameLookup(true);
 
-  // Template names cannot appear inside an Objective-C class or object type
-  // or a vector type.
-  //
-  // FIXME: This is wrong. For example:
-  //
-  //   template<typename T> using Vec = T __attribute__((ext_vector_type(4)));
-  //   Vec<int> vi;
-  //   vi.Vec<int>::~Vec<int>();
-  //
-  // ... should be accepted but we will not treat 'Vec' as a template name
-  // here. The right thing to do would be to check if the name is a valid
-  // vector component name, and look up a template name if not. And similarly
-  // for lookups into Objective-C class and object types, where the same
-  // problem can arise.
-  if (!ObjectType.isNull() && (ObjectType->isVectorType() ||
-                               ObjectType->isObjCObjectOrInterfaceType())) {
-    Found.clear();
-    return false;
-  }
-
-  LookupParsedName(Found, S, &SS, ObjectType,
-                   /*AllowBuiltinCreation=*/false, EnteringContext);
+  // Determine where to perform name lookup
+  DeclContext *LookupCtx = nullptr;
+  bool IsDependent = false;
+  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.isEmpty() && "ObjectType and scope specifier cannot coexist");
+    LookupCtx = computeDeclContext(ObjectType);
+    IsDependent = !LookupCtx && ObjectType->isDependentType();
+    assert((IsDependent || !ObjectType->isIncompleteType() ||
+            !ObjectType->getAs<TagType>() ||
+            ObjectType->castAs<TagType>()->isBeingDefined()) &&
+           "Caller should have completed object type");
+
+    // Template names cannot appear inside an Objective-C class or object type
+    // or a vector type.
+    //
+    // FIXME: This is wrong. For example:
+    //
+    //   template<typename T> using Vec = T __attribute__((ext_vector_type(4)));
+    //   Vec<int> vi;
+    //   vi.Vec<int>::~Vec<int>();
+    //
+    // ... should be accepted but we will not treat 'Vec' as a template name
+    // here. The right thing to do would be to check if the name is a valid
+    // vector component name, and look up a template name if not. And similarly
+    // for lookups into Objective-C class and object types, where the same
+    // problem can arise.
+    if (ObjectType->isObjCObjectOrInterfaceType() ||
+        ObjectType->isVectorType()) {
+      Found.clear();
+      return false;
+    }
+  } 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 && isDependentScopeSpecifier(SS);
 
-  // C++ [basic.lookup.qual.general]p3:
-  //   [...] Unless otherwise specified, a qualified name undergoes qualified
-  //   name lookup in its lookup context from the point where it appears unless
-  //   the lookup context either is dependent and is not the current
-  //   instantiation or is not a class or class template.
-  //
-  // The lookup context is dependent and either:
-  // - it is not the current instantiation, or
-  // - it is the current instantiation, it has at least one dependent base
-  //   class, and qualified lookup found nothing.
-  //
-  // If this is a member-qualified name that is the terminal name of a
-  // nested-name-specifier, we perform unqualified lookup and store the results
-  // so we can replicate the lookup during instantiation. The results of the
-  // unqualified loookup are *not* used to determine whether '<' is interpreted
-  // as the delimiter of a template-argument-list.
-  //
-  // For example:
-  //
-  //   template<typename T>
-  //   struct A {
-  //     int x;
-  //   };
-  //
-  //   template<typename T>
-  //   using B = A<T>;
-  //
-  //   template<typename T>
-  //   void f(A<T> a, A<int> b) {
-  //     a.B<T>::x; // error: missing 'template' before 'B'
-  //     b.B<int>::x; // ok, lookup context is not dependent
-  //   }
-  if (Found.wasNotFoundInCurrentInstantiation())
-    return false;
+    // The declaration context must be complete.
+    if (LookupCtx && RequireCompleteDeclContext(SS, LookupCtx))
+      return true;
+  }
 
   bool ObjectTypeSearchedInScope = false;
-
-  // C++ [basic.lookup.qual.general]p2:
-  //   A member-qualified name is the (unique) component name, if any, of
-  //   - an unqualified-id or
-  //   - a nested-name-specifier of the form type-name :: or namespace-name ::
-  //   in the id-expression of a class member access expression.
-  //
-  // C++ [basic.lookup.qual.general]p3:
-  //   [...] If nothing is found by qualified lookup for a member-qualified
-  //   name that is the terminal name of a nested-name-specifier and is not
-  //   dependent, it undergoes unqualified lookup.
-  //
-  // In 'x.A::B::y', 'A' will undergo unqualified lookup if qualified lookup
-  // in the type of 'x' finds nothing. If the lookup context is dependent,
-  // we perform the unqualified lookup in the template definition context
-  // and store the results so we can replicate the lookup during instantiation.
-  if (MayBeNNS && Found.empty() && !ObjectType.isNull()) {
-    if (S) {
+  bool AllowFunctionTemplatesInLookup = true;
+  if (LookupCtx) {
+    // Perform "qualified" name lookup into the declaration context we
+    // computed, which is either the type of the base of a member access
+    // expression or the declaration context associated with a prior
+    // nested-name-specifier.
+    LookupQualifiedName(Found, LookupCtx);
+
+    // FIXME: The C++ standard does not clearly specify what happens in the
+    // case where the object type is dependent, and implementations vary. In
+    // Clang, we treat a name after a . or -> as a template-name if lookup
+    // finds a non-dependent member or member of the current instantiation that
+    // is a type template, or finds no such members and lookup in the context
+    // of the postfix-expression finds a type template. In the latter case, the
+    // name is nonetheless dependent, and we may resolve it to a member of an
+    // unknown specialization when we come to instantiate the template.
+    IsDependent |= Found.wasNotFoundInCurrentInstantiation();
+  }
+
+  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
+    //   identifier must be looked up to determine whether the < is the
+    //   beginning of a template argument list (14.2) or a less-than operator.
+    //   The identifier is first looked up in the class of the object
+    //   expression. If the identifier is not found, it is then looked up in
+    //   the context of the entire postfix-expression and shall name a class
+    //   template.
+    if (S)
       LookupName(Found, S);
-    } else if (!SS.getUnqualifiedLookups().empty()) {
-      Found.addAllDecls(SS.getUnqualifiedLookups());
-      Found.resolveKind();
+
+    if (!ObjectType.isNull()) {
+      //  FIXME: We should filter out all non-type templates here, particularly
+      //  variable templates and concepts. But the exclusion of alias templates
+      //  and template template parameters is a wording defect.
+      AllowFunctionTemplatesInLookup = false;
+      ObjectTypeSearchedInScope = true;
     }
-    ObjectTypeSearchedInScope = true;
+
+    IsDependent |= Found.wasNotFoundInCurrentInstantiation();
   }
 
   if (Found.isAmbiguous())
@@ -489,7 +494,7 @@ bool Sema::LookupTemplateName(LookupResult &Found, Scope *S, CXXScopeSpec &SS,
         getLangOpts().CPlusPlus20 && llvm::all_of(Found, [](NamedDecl *ND) {
           return isa<FunctionDecl>(ND->getUnderlyingDecl());
         });
-    if (AllFunctions || Found.empty()) {
+    if (AllFunctions || (Found.empty() && !IsDependent)) {
       // If lookup found any functions, or if this is a name that can only be
       // used for a function, then strongly assume this is a function
       // template-id.
@@ -501,15 +506,11 @@ bool Sema::LookupTemplateName(LookupResult &Found, Scope *S, CXXScopeSpec &SS,
     }
   }
 
-  if (Found.empty() && AllowTypoCorrection) {
+  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();
-    DeclContext *LookupCtx =
-        SS.isSet()
-            ? computeDeclContext(SS, EnteringContext)
-            : (!ObjectType.isNull() ? computeDeclContext(ObjectType) : nullptr);
     // Simple filter callback that, for keywords, only accepts the C++ *_cast
     DefaultFilterCCC FilterCCC{};
     FilterCCC.WantTypeSpecifiers = false;
@@ -542,8 +543,13 @@ bool Sema::LookupTemplateName(LookupResult &Found, Scope *S, CXXScopeSpec &SS,
 
   NamedDecl *ExampleLookupResult =
       Found.empty() ? nullptr : Found.getRepresentativeDecl();
-  FilterAcceptableTemplateNames(Found);
+  FilterAcceptableTemplateNames(Found, AllowFunctionTemplatesInLookup);
   if (Found.empty()) {
+    if (IsDependent) {
+      Found.setNotFoundInCurrentInstantiation();
+      return false;
+    }
+
     // If a 'template' keyword was used, a lookup that finds only non-template
     // names is an error.
     if (ExampleLookupResult && RequiredTemplate) {
@@ -735,7 +741,7 @@ Sema::ActOnDependentIdExpression(const CXXScopeSpec &SS,
         /*IsArrow=*/!Context.getLangOpts().HLSL,
         /*OperatorLoc=*/SourceLocation(),
         /*QualifierLoc=*/NestedNameSpecifierLoc(), TemplateKWLoc,
-        /*UnqualifiedLookups=*/std::nullopt, NameInfo, TemplateArgs);
+        /*FirstQualifierFoundInScope=*/nullptr, NameInfo, TemplateArgs);
   }
   return BuildDependentDeclRefExpr(SS, TemplateKWLoc, NameInfo, TemplateArgs);
 }
@@ -4470,10 +4476,14 @@ ExprResult Sema::BuildQualifiedTemplateIdExpr(
   return BuildTemplateIdExpr(SS, TemplateKWLoc, R, /*ADL=*/false, TemplateArgs);
 }
 
-TemplateNameKind Sema::ActOnTemplateName(
-    Scope *S, CXXScopeSpec &SS, SourceLocation TemplateKWLoc,
-    const UnqualifiedId &Name, ParsedType ObjectType, bool EnteringContext,
-    TemplateTy &Result, bool AllowInjectedClassName, bool MayBeNNS) {
+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 ?
@@ -4508,10 +4518,9 @@ TemplateNameKind Sema::ActOnTemplateName(
   // "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,
-                     /*Disambiguation=*/false, MayBeNNS);
+  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);
@@ -4550,8 +4559,7 @@ TemplateNameKind Sema::ActOnTemplateName(
                                    ? RequiredTemplateKind(TemplateKWLoc)
                                    : TemplateNameIsRequired;
     if (!LookupTemplateName(R, S, SS, ObjectType.get(), EnteringContext, RTK,
-                            /*ATK=*/nullptr, /*AllowTypoCorrection=*/false,
-                            MayBeNNS) &&
+                            /*ATK=*/nullptr, /*AllowTypoCorrection=*/false) &&
         !R.isAmbiguous()) {
       if (LookupCtx)
         Diag(Name.getBeginLoc(), diag::err_no_member)

diff  --git a/clang/lib/Sema/SemaTemplateInstantiate.cpp b/clang/lib/Sema/SemaTemplateInstantiate.cpp
index 64c5a16b2e4c3..a7bc6749c5852 100644
--- a/clang/lib/Sema/SemaTemplateInstantiate.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiate.cpp
@@ -1515,11 +1515,12 @@ namespace {
                                    NestedNameSpecifierLoc QualifierLoc,
                                    QualType T);
 
-    TemplateName TransformTemplateName(CXXScopeSpec &SS, TemplateName Name,
-                                       SourceLocation NameLoc,
-                                       QualType ObjectType = QualType(),
-                                       bool AllowInjectedClassName = false,
-                                       bool MayBeNNS = false);
+    TemplateName
+    TransformTemplateName(CXXScopeSpec &SS, TemplateName Name,
+                          SourceLocation NameLoc,
+                          QualType ObjectType = QualType(),
+                          NamedDecl *FirstQualifierInScope = nullptr,
+                          bool AllowInjectedClassName = false);
 
     const CXXAssumeAttr *TransformCXXAssumeAttr(const CXXAssumeAttr *AA);
     const LoopHintAttr *TransformLoopHintAttr(const LoopHintAttr *LH);
@@ -1951,7 +1952,8 @@ TemplateInstantiator::RebuildElaboratedType(SourceLocation KeywordLoc,
 
 TemplateName TemplateInstantiator::TransformTemplateName(
     CXXScopeSpec &SS, TemplateName Name, SourceLocation NameLoc,
-    QualType ObjectType, bool AllowInjectedClassName, bool MayBeNNS) {
+    QualType ObjectType, NamedDecl *FirstQualifierInScope,
+    bool AllowInjectedClassName) {
   if (TemplateTemplateParmDecl *TTP
        = dyn_cast_or_null<TemplateTemplateParmDecl>(Name.getAsTemplateDecl())) {
     if (TTP->getDepth() < TemplateArgs.getNumLevels()) {
@@ -2023,7 +2025,8 @@ TemplateName TemplateInstantiator::TransformTemplateName(
   }
 
   return inherited::TransformTemplateName(SS, Name, NameLoc, ObjectType,
-                                          AllowInjectedClassName, MayBeNNS);
+                                          FirstQualifierInScope,
+                                          AllowInjectedClassName);
 }
 
 ExprResult

diff  --git a/clang/lib/Sema/TreeTransform.h b/clang/lib/Sema/TreeTransform.h
index f6021440cda69..655f248d11383 100644
--- a/clang/lib/Sema/TreeTransform.h
+++ b/clang/lib/Sema/TreeTransform.h
@@ -541,9 +541,10 @@ class TreeTransform {
   /// By default, transforms all of the types and declarations within the
   /// nested-name-specifier. Subclasses may override this function to provide
   /// alternate behavior.
-  NestedNameSpecifierLoc TransformNestedNameSpecifierLoc(
-      NestedNameSpecifierLoc NNS, QualType ObjectType = QualType(),
-      ArrayRef<DeclAccessPair> UnqualifiedLookups = std::nullopt);
+  NestedNameSpecifierLoc
+  TransformNestedNameSpecifierLoc(NestedNameSpecifierLoc NNS,
+                                  QualType ObjectType = QualType(),
+                                  NamedDecl *FirstQualifierInScope = nullptr);
 
   /// Transform the given declaration name.
   ///
@@ -584,11 +585,12 @@ class TreeTransform {
   /// By default, transforms the template name by transforming the declarations
   /// and nested-name-specifiers that occur within the template name.
   /// Subclasses may override this function to provide alternate behavior.
-  TemplateName TransformTemplateName(CXXScopeSpec &SS, TemplateName Name,
-                                     SourceLocation NameLoc,
-                                     QualType ObjectType = QualType(),
-                                     bool AllowInjectedClassName = false,
-                                     bool MayBeNNS = false);
+  TemplateName
+  TransformTemplateName(CXXScopeSpec &SS, TemplateName Name,
+                        SourceLocation NameLoc,
+                        QualType ObjectType = QualType(),
+                        NamedDecl *FirstQualifierInScope = nullptr,
+                        bool AllowInjectedClassName = false);
 
   /// Transform the given template argument.
   ///
@@ -1138,8 +1140,8 @@ class TreeTransform {
     CXXScopeSpec SS;
     SS.Adopt(QualifierLoc);
     TemplateName InstName = getDerived().RebuildTemplateName(
-        SS, TemplateKWLoc, *Name, NameLoc, QualType(), AllowInjectedClassName,
-        /*MayBeNNS=*/false);
+        SS, TemplateKWLoc, *Name, NameLoc, QualType(), nullptr,
+        AllowInjectedClassName);
 
     if (InstName.isNull())
       return QualType();
@@ -1310,7 +1312,8 @@ class TreeTransform {
                                    SourceLocation TemplateKWLoc,
                                    const IdentifierInfo &Name,
                                    SourceLocation NameLoc, QualType ObjectType,
-                                   bool AllowInjectedClassName, bool MayBeNNS);
+                                   NamedDecl *FirstQualifierInScope,
+                                   bool AllowInjectedClassName);
 
   /// Build a new template name given a nested name specifier and the
   /// overloaded operator name that is referred to as a template.
@@ -2846,14 +2849,15 @@ class TreeTransform {
   ///
   /// By default, performs semantic analysis to build the new expression.
   /// Subclasses may override this routine to provide 
diff erent behavior.
-  ExprResult
-  RebuildMemberExpr(Expr *Base, SourceLocation OpLoc, bool isArrow,
-                    NestedNameSpecifierLoc QualifierLoc,
-                    SourceLocation TemplateKWLoc,
-                    const DeclarationNameInfo &MemberNameInfo,
-                    ValueDecl *Member, NamedDecl *FoundDecl,
-                    const TemplateArgumentListInfo *ExplicitTemplateArgs,
-                    ArrayRef<DeclAccessPair> UnqualifiedLookups) {
+  ExprResult RebuildMemberExpr(Expr *Base, SourceLocation OpLoc,
+                               bool isArrow,
+                               NestedNameSpecifierLoc QualifierLoc,
+                               SourceLocation TemplateKWLoc,
+                               const DeclarationNameInfo &MemberNameInfo,
+                               ValueDecl *Member,
+                               NamedDecl *FoundDecl,
+                        const TemplateArgumentListInfo *ExplicitTemplateArgs,
+                               NamedDecl *FirstQualifierInScope) {
     ExprResult BaseResult = getSema().PerformMemberExprBaseConversion(Base,
                                                                       isArrow);
     if (!Member->getDeclName()) {
@@ -2890,7 +2894,6 @@ class TreeTransform {
 
     CXXScopeSpec SS;
     SS.Adopt(QualifierLoc);
-    SS.setUnqualifiedLookups(UnqualifiedLookups);
 
     Base = BaseResult.get();
     if (Base->containsErrors())
@@ -2923,9 +2926,10 @@ class TreeTransform {
     }
 
     return getSema().BuildMemberReferenceExpr(Base, BaseType, OpLoc, isArrow,
-                                              SS, TemplateKWLoc, R,
-                                              ExplicitTemplateArgs,
-                                              /*S=*/nullptr);
+                                              SS, TemplateKWLoc,
+                                              FirstQualifierInScope,
+                                              R, ExplicitTemplateArgs,
+                                              /*S*/nullptr);
   }
 
   /// Build a new binary operator expression.
@@ -2998,9 +3002,10 @@ class TreeTransform {
     CXXScopeSpec SS;
     DeclarationNameInfo NameInfo(&Accessor, AccessorLoc);
     return getSema().BuildMemberReferenceExpr(
-        Base, Base->getType(), OpLoc, IsArrow, SS,
-        /*TemplateKWLoc=*/SourceLocation(), NameInfo,
-        /*TemplateArgs=*/nullptr, /*S=*/nullptr);
+        Base, Base->getType(), OpLoc, IsArrow, SS, SourceLocation(),
+        /*FirstQualifierInScope*/ nullptr, NameInfo,
+        /* TemplateArgs */ nullptr,
+        /*S*/ nullptr);
   }
 
   /// Build a new initializer list expression.
@@ -3568,37 +3573,46 @@ class TreeTransform {
   ///
   /// By default, performs semantic analysis to build the new expression.
   /// Subclasses may override this routine to provide 
diff erent behavior.
-  ExprResult RebuildCXXDependentScopeMemberExpr(
-      Expr *BaseE, QualType BaseType, bool IsArrow, SourceLocation OperatorLoc,
-      NestedNameSpecifierLoc QualifierLoc, SourceLocation TemplateKWLoc,
-      ArrayRef<DeclAccessPair> UnqualifiedLookups,
-      const DeclarationNameInfo &MemberNameInfo,
-      const TemplateArgumentListInfo *TemplateArgs) {
+  ExprResult RebuildCXXDependentScopeMemberExpr(Expr *BaseE,
+                                                QualType BaseType,
+                                                bool IsArrow,
+                                                SourceLocation OperatorLoc,
+                                          NestedNameSpecifierLoc QualifierLoc,
+                                                SourceLocation TemplateKWLoc,
+                                            NamedDecl *FirstQualifierInScope,
+                                   const DeclarationNameInfo &MemberNameInfo,
+                              const TemplateArgumentListInfo *TemplateArgs) {
     CXXScopeSpec SS;
     SS.Adopt(QualifierLoc);
-    SS.setUnqualifiedLookups(UnqualifiedLookups);
 
-    return SemaRef.BuildMemberReferenceExpr(
-        BaseE, BaseType, OperatorLoc, IsArrow, SS, TemplateKWLoc,
-        MemberNameInfo, TemplateArgs, /*S=*/nullptr);
+    return SemaRef.BuildMemberReferenceExpr(BaseE, BaseType,
+                                            OperatorLoc, IsArrow,
+                                            SS, TemplateKWLoc,
+                                            FirstQualifierInScope,
+                                            MemberNameInfo,
+                                            TemplateArgs, /*S*/nullptr);
   }
 
   /// Build a new member reference expression.
   ///
   /// By default, performs semantic analysis to build the new expression.
   /// Subclasses may override this routine to provide 
diff erent behavior.
-  ExprResult RebuildUnresolvedMemberExpr(
-      Expr *BaseE, QualType BaseType, SourceLocation OperatorLoc, bool IsArrow,
-      NestedNameSpecifierLoc QualifierLoc, SourceLocation TemplateKWLoc,
-      ArrayRef<DeclAccessPair> UnqualifiedLookups, LookupResult &R,
-      const TemplateArgumentListInfo *TemplateArgs) {
+  ExprResult RebuildUnresolvedMemberExpr(Expr *BaseE, QualType BaseType,
+                                         SourceLocation OperatorLoc,
+                                         bool IsArrow,
+                                         NestedNameSpecifierLoc QualifierLoc,
+                                         SourceLocation TemplateKWLoc,
+                                         NamedDecl *FirstQualifierInScope,
+                                         LookupResult &R,
+                                const TemplateArgumentListInfo *TemplateArgs) {
     CXXScopeSpec SS;
     SS.Adopt(QualifierLoc);
-    SS.setUnqualifiedLookups(UnqualifiedLookups);
 
-    return SemaRef.BuildMemberReferenceExpr(BaseE, BaseType, OperatorLoc,
-                                            IsArrow, SS, TemplateKWLoc, R,
-                                            TemplateArgs, /*S=*/nullptr);
+    return SemaRef.BuildMemberReferenceExpr(BaseE, BaseType,
+                                            OperatorLoc, IsArrow,
+                                            SS, TemplateKWLoc,
+                                            FirstQualifierInScope,
+                                            R, TemplateArgs, /*S*/nullptr);
   }
 
   /// Build a new noexcept expression.
@@ -3817,8 +3831,10 @@ class TreeTransform {
     DeclarationNameInfo NameInfo(Ivar->getDeclName(), IvarLoc);
     ExprResult Result = getSema().BuildMemberReferenceExpr(
         BaseArg, BaseArg->getType(),
-        /*FIXME:*/ IvarLoc, IsArrow, SS, /*TemplateKWLoc=*/SourceLocation(),
-        NameInfo, /*TemplateArgs=*/nullptr, /*S=*/nullptr);
+        /*FIXME:*/ IvarLoc, IsArrow, SS, SourceLocation(),
+        /*FirstQualifierInScope=*/nullptr, NameInfo,
+        /*TemplateArgs=*/nullptr,
+        /*S=*/nullptr);
     if (IsFreeIvar && Result.isUsable())
       cast<ObjCIvarRefExpr>(Result.get())->setIsFreeIvar(IsFreeIvar);
     return Result;
@@ -3833,12 +3849,14 @@ class TreeTransform {
                                         SourceLocation PropertyLoc) {
     CXXScopeSpec SS;
     DeclarationNameInfo NameInfo(Property->getDeclName(), PropertyLoc);
-    return getSema().BuildMemberReferenceExpr(
-        BaseArg, BaseArg->getType(),
-        /*FIXME:*/ PropertyLoc,
-        /*IsArrow=*/false, SS, /*TemplateKWLoc=*/SourceLocation(), NameInfo,
-        /*TemplateArgs=*/nullptr,
-        /*S=*/nullptr);
+    return getSema().BuildMemberReferenceExpr(BaseArg, BaseArg->getType(),
+                                              /*FIXME:*/PropertyLoc,
+                                              /*IsArrow=*/false,
+                                              SS, SourceLocation(),
+                                              /*FirstQualifierInScope=*/nullptr,
+                                              NameInfo,
+                                              /*TemplateArgs=*/nullptr,
+                                              /*S=*/nullptr);
   }
 
   /// Build a new Objective-C property reference expression.
@@ -3865,11 +3883,13 @@ class TreeTransform {
                                 SourceLocation OpLoc, bool IsArrow) {
     CXXScopeSpec SS;
     DeclarationNameInfo NameInfo(&getSema().Context.Idents.get("isa"), IsaLoc);
-    return getSema().BuildMemberReferenceExpr(
-        BaseArg, BaseArg->getType(), OpLoc, IsArrow, SS,
-        /*TemplateKWLoc=*/SourceLocation(), NameInfo,
-        /*TemplateArgs=*/nullptr,
-        /*S=*/nullptr);
+    return getSema().BuildMemberReferenceExpr(BaseArg, BaseArg->getType(),
+                                              OpLoc, IsArrow,
+                                              SS, SourceLocation(),
+                                              /*FirstQualifierInScope=*/nullptr,
+                                              NameInfo,
+                                              /*TemplateArgs=*/nullptr,
+                                              /*S=*/nullptr);
   }
 
   /// Build a new shuffle vector expression.
@@ -4034,14 +4054,18 @@ class TreeTransform {
   }
 
 private:
-  TypeLoc TransformTypeInObjectScope(TypeLoc TL, QualType ObjectType,
+  TypeLoc TransformTypeInObjectScope(TypeLoc TL,
+                                     QualType ObjectType,
+                                     NamedDecl *FirstQualifierInScope,
                                      CXXScopeSpec &SS);
 
   TypeSourceInfo *TransformTypeInObjectScope(TypeSourceInfo *TSInfo,
                                              QualType ObjectType,
+                                             NamedDecl *FirstQualifierInScope,
                                              CXXScopeSpec &SS);
 
   TypeSourceInfo *TransformTSIInObjectScope(TypeLoc TL, QualType ObjectType,
+                                            NamedDecl *FirstQualifierInScope,
                                             CXXScopeSpec &SS);
 
   QualType TransformDependentNameType(TypeLocBuilder &TLB,
@@ -4360,7 +4384,7 @@ Sema::ConditionResult TreeTransform<Derived>::TransformCondition(
 template <typename Derived>
 NestedNameSpecifierLoc TreeTransform<Derived>::TransformNestedNameSpecifierLoc(
     NestedNameSpecifierLoc NNS, QualType ObjectType,
-    ArrayRef<DeclAccessPair> UnqualifiedLookups) {
+    NamedDecl *FirstQualifierInScope) {
   SmallVector<NestedNameSpecifierLoc, 4> Qualifiers;
 
   auto insertNNS = [&Qualifiers](NestedNameSpecifierLoc NNS) {
@@ -4371,8 +4395,6 @@ NestedNameSpecifierLoc TreeTransform<Derived>::TransformNestedNameSpecifierLoc(
   insertNNS(NNS);
 
   CXXScopeSpec SS;
-  SS.setUnqualifiedLookups(UnqualifiedLookups);
-
   while (!Qualifiers.empty()) {
     NestedNameSpecifierLoc Q = Qualifiers.pop_back_val();
     NestedNameSpecifier *QNNS = Q.getNestedNameSpecifier();
@@ -4382,9 +4404,8 @@ NestedNameSpecifierLoc TreeTransform<Derived>::TransformNestedNameSpecifierLoc(
       Sema::NestedNameSpecInfo IdInfo(QNNS->getAsIdentifier(),
                                       Q.getLocalBeginLoc(), Q.getLocalEndLoc(),
                                       ObjectType);
-      if (SemaRef.BuildCXXNestedNameSpecifier(/*Scope=*/nullptr, IdInfo,
-                                              /*EnteringContext=*/false, SS,
-                                              /*ErrorRecoveryLookup=*/false))
+      if (SemaRef.BuildCXXNestedNameSpecifier(/*Scope=*/nullptr, IdInfo, false,
+                                              SS, FirstQualifierInScope, false))
         return NestedNameSpecifierLoc();
       break;
     }
@@ -4422,7 +4443,8 @@ NestedNameSpecifierLoc TreeTransform<Derived>::TransformNestedNameSpecifierLoc(
 
     case NestedNameSpecifier::TypeSpecWithTemplate:
     case NestedNameSpecifier::TypeSpec: {
-      TypeLoc TL = TransformTypeInObjectScope(Q.getTypeLoc(), ObjectType, SS);
+      TypeLoc TL = TransformTypeInObjectScope(Q.getTypeLoc(), ObjectType,
+                                              FirstQualifierInScope, SS);
 
       if (!TL)
         return NestedNameSpecifierLoc();
@@ -4455,7 +4477,7 @@ NestedNameSpecifierLoc TreeTransform<Derived>::TransformNestedNameSpecifierLoc(
     }
 
     // The qualifier-in-scope and object type only apply to the leftmost entity.
-    SS.setUnqualifiedLookups(std::nullopt);
+    FirstQualifierInScope = nullptr;
     ObjectType = QualType();
   }
 
@@ -4538,10 +4560,14 @@ ::TransformDeclarationNameInfo(const DeclarationNameInfo &NameInfo) {
   llvm_unreachable("Unknown name kind.");
 }
 
-template <typename Derived>
-TemplateName TreeTransform<Derived>::TransformTemplateName(
-    CXXScopeSpec &SS, TemplateName Name, SourceLocation NameLoc,
-    QualType ObjectType, bool AllowInjectedClassName, bool MayBeNNS) {
+template<typename Derived>
+TemplateName
+TreeTransform<Derived>::TransformTemplateName(CXXScopeSpec &SS,
+                                              TemplateName Name,
+                                              SourceLocation NameLoc,
+                                              QualType ObjectType,
+                                              NamedDecl *FirstQualifierInScope,
+                                              bool AllowInjectedClassName) {
   if (QualifiedTemplateName *QTN = Name.getAsQualifiedTemplateName()) {
     TemplateDecl *Template = QTN->getUnderlyingTemplate().getAsTemplateDecl();
     assert(Template && "qualified template name must refer to a template");
@@ -4565,7 +4591,7 @@ TemplateName TreeTransform<Derived>::TransformTemplateName(
     if (SS.getScopeRep()) {
       // These apply to the scope specifier, not the template.
       ObjectType = QualType();
-      SS.setUnqualifiedLookups(std::nullopt);
+      FirstQualifierInScope = nullptr;
     }
 
     if (!getDerived().AlwaysRebuild() &&
@@ -4577,9 +4603,13 @@ TemplateName TreeTransform<Derived>::TransformTemplateName(
     SourceLocation TemplateKWLoc = NameLoc;
 
     if (DTN->isIdentifier()) {
-      return getDerived().RebuildTemplateName(
-          SS, TemplateKWLoc, *DTN->getIdentifier(), NameLoc, ObjectType,
-          AllowInjectedClassName, MayBeNNS);
+      return getDerived().RebuildTemplateName(SS,
+                                              TemplateKWLoc,
+                                              *DTN->getIdentifier(),
+                                              NameLoc,
+                                              ObjectType,
+                                              FirstQualifierInScope,
+                                              AllowInjectedClassName);
     }
 
     return getDerived().RebuildTemplateName(SS, TemplateKWLoc,
@@ -5123,31 +5153,39 @@ QualType TreeTransform<Derived>::RebuildQualifiedType(QualType T,
   return SemaRef.BuildQualifiedType(T, Loc, Quals);
 }
 
-template <typename Derived>
-TypeLoc TreeTransform<Derived>::TransformTypeInObjectScope(TypeLoc TL,
-                                                           QualType ObjectType,
-                                                           CXXScopeSpec &SS) {
+template<typename Derived>
+TypeLoc
+TreeTransform<Derived>::TransformTypeInObjectScope(TypeLoc TL,
+                                                   QualType ObjectType,
+                                                   NamedDecl *UnqualLookup,
+                                                   CXXScopeSpec &SS) {
   if (getDerived().AlreadyTransformed(TL.getType()))
     return TL;
 
-  TypeSourceInfo *TSI = TransformTSIInObjectScope(TL, ObjectType, SS);
+  TypeSourceInfo *TSI =
+      TransformTSIInObjectScope(TL, ObjectType, UnqualLookup, SS);
   if (TSI)
     return TSI->getTypeLoc();
   return TypeLoc();
 }
 
-template <typename Derived>
-TypeSourceInfo *TreeTransform<Derived>::TransformTypeInObjectScope(
-    TypeSourceInfo *TSInfo, QualType ObjectType, CXXScopeSpec &SS) {
+template<typename Derived>
+TypeSourceInfo *
+TreeTransform<Derived>::TransformTypeInObjectScope(TypeSourceInfo *TSInfo,
+                                                   QualType ObjectType,
+                                                   NamedDecl *UnqualLookup,
+                                                   CXXScopeSpec &SS) {
   if (getDerived().AlreadyTransformed(TSInfo->getType()))
     return TSInfo;
 
-  return TransformTSIInObjectScope(TSInfo->getTypeLoc(), ObjectType, SS);
+  return TransformTSIInObjectScope(TSInfo->getTypeLoc(), ObjectType,
+                                   UnqualLookup, SS);
 }
 
 template <typename Derived>
 TypeSourceInfo *TreeTransform<Derived>::TransformTSIInObjectScope(
-    TypeLoc TL, QualType ObjectType, CXXScopeSpec &SS) {
+    TypeLoc TL, QualType ObjectType, NamedDecl *UnqualLookup,
+    CXXScopeSpec &SS) {
   QualType T = TL.getType();
   assert(!getDerived().AlreadyTransformed(T));
 
@@ -5160,7 +5198,7 @@ TypeSourceInfo *TreeTransform<Derived>::TransformTSIInObjectScope(
 
     TemplateName Template = getDerived().TransformTemplateName(
         SS, SpecTL.getTypePtr()->getTemplateName(), SpecTL.getTemplateNameLoc(),
-        ObjectType, /*AllowInjectedClassName=*/true, /*MayBeNNS=*/true);
+        ObjectType, UnqualLookup, /*AllowInjectedClassName*/true);
     if (Template.isNull())
       return nullptr;
 
@@ -5170,11 +5208,13 @@ TypeSourceInfo *TreeTransform<Derived>::TransformTSIInObjectScope(
     DependentTemplateSpecializationTypeLoc SpecTL =
         TL.castAs<DependentTemplateSpecializationTypeLoc>();
 
-    TemplateName Template = getDerived().RebuildTemplateName(
-        SS, SpecTL.getTemplateKeywordLoc(),
-        *SpecTL.getTypePtr()->getIdentifier(), SpecTL.getTemplateNameLoc(),
-        ObjectType,
-        /*AllowInjectedClassName=*/true, /*MayBeNNS=*/true);
+    TemplateName Template
+      = getDerived().RebuildTemplateName(SS,
+                                         SpecTL.getTemplateKeywordLoc(),
+                                         *SpecTL.getTypePtr()->getIdentifier(),
+                                         SpecTL.getTemplateNameLoc(),
+                                         ObjectType, UnqualLookup,
+                                         /*AllowInjectedClassName*/true);
     if (Template.isNull())
       return nullptr;
 
@@ -12318,8 +12358,7 @@ TreeTransform<Derived>::TransformMemberExpr(MemberExpr *E) {
   // first-qualifier-in-scope here, just in case we had a dependent
   // base (and therefore couldn't do the check) and a
   // nested-name-qualifier (and therefore could do the lookup).
-  ArrayRef<DeclAccessPair> UnqualifiedLookups;
-
+  NamedDecl *FirstQualifierInScope = nullptr;
   DeclarationNameInfo MemberNameInfo = E->getMemberNameInfo();
   if (MemberNameInfo.getName()) {
     MemberNameInfo = getDerived().TransformDeclarationNameInfo(MemberNameInfo);
@@ -12327,11 +12366,16 @@ TreeTransform<Derived>::TransformMemberExpr(MemberExpr *E) {
       return ExprError();
   }
 
-  return getDerived().RebuildMemberExpr(
-      Base.get(), FakeOperatorLoc, E->isArrow(), QualifierLoc, TemplateKWLoc,
-      MemberNameInfo, Member, FoundDecl,
-      (E->hasExplicitTemplateArgs() ? &TransArgs : nullptr),
-      UnqualifiedLookups);
+  return getDerived().RebuildMemberExpr(Base.get(), FakeOperatorLoc,
+                                        E->isArrow(),
+                                        QualifierLoc,
+                                        TemplateKWLoc,
+                                        MemberNameInfo,
+                                        Member,
+                                        FoundDecl,
+                                        (E->hasExplicitTemplateArgs()
+                                           ? &TransArgs : nullptr),
+                                        FirstQualifierInScope);
 }
 
 template<typename Derived>
@@ -13458,8 +13502,9 @@ TreeTransform<Derived>::TransformCXXPseudoDestructorExpr(
 
   PseudoDestructorTypeStorage Destroyed;
   if (E->getDestroyedTypeInfo()) {
-    TypeSourceInfo *DestroyedTypeInfo = getDerived().TransformTypeInObjectScope(
-        E->getDestroyedTypeInfo(), ObjectType, SS);
+    TypeSourceInfo *DestroyedTypeInfo
+      = getDerived().TransformTypeInObjectScope(E->getDestroyedTypeInfo(),
+                                                ObjectType, nullptr, SS);
     if (!DestroyedTypeInfo)
       return ExprError();
     Destroyed = DestroyedTypeInfo;
@@ -13485,7 +13530,7 @@ TreeTransform<Derived>::TransformCXXPseudoDestructorExpr(
   if (E->getScopeTypeInfo()) {
     CXXScopeSpec EmptySS;
     ScopeTypeInfo = getDerived().TransformTypeInObjectScope(
-        E->getScopeTypeInfo(), ObjectType, EmptySS);
+                      E->getScopeTypeInfo(), ObjectType, nullptr, EmptySS);
     if (!ScopeTypeInfo)
       return ExprError();
   }
@@ -14746,17 +14791,19 @@ TreeTransform<Derived>::TransformCXXDependentScopeMemberExpr(
     ObjectType = BaseType->castAs<PointerType>()->getPointeeType();
   }
 
-  UnresolvedSet<4> UnqualifiedLookups;
-  for (auto D : E->unqualified_lookups()) {
-    if (NamedDecl *InstD = getDerived().TransformFirstQualifierInScope(
-            D.getDecl(), E->getQualifierLoc().getBeginLoc()))
-      UnqualifiedLookups.addDecl(InstD);
-  }
+  // Transform the first part of the nested-name-specifier that qualifies
+  // the member name.
+  NamedDecl *FirstQualifierInScope
+    = getDerived().TransformFirstQualifierInScope(
+                                            E->getFirstQualifierFoundInScope(),
+                                            E->getQualifierLoc().getBeginLoc());
 
   NestedNameSpecifierLoc QualifierLoc;
   if (E->getQualifier()) {
-    QualifierLoc = getDerived().TransformNestedNameSpecifierLoc(
-        E->getQualifierLoc(), ObjectType, UnqualifiedLookups.pairs());
+    QualifierLoc
+      = getDerived().TransformNestedNameSpecifierLoc(E->getQualifierLoc(),
+                                                     ObjectType,
+                                                     FirstQualifierInScope);
     if (!QualifierLoc)
       return ExprError();
   }
@@ -14775,16 +14822,23 @@ TreeTransform<Derived>::TransformCXXDependentScopeMemberExpr(
   if (!E->hasExplicitTemplateArgs()) {
     // This is a reference to a member without an explicitly-specified
     // template argument list. Optimize for this common case.
-    if (!getDerived().AlwaysRebuild() && Base.get() == OldBase &&
-        BaseType == E->getBaseType() && QualifierLoc == E->getQualifierLoc() &&
+    if (!getDerived().AlwaysRebuild() &&
+        Base.get() == OldBase &&
+        BaseType == E->getBaseType() &&
+        QualifierLoc == E->getQualifierLoc() &&
         NameInfo.getName() == E->getMember() &&
-        UnqualifiedLookups.pairs() == E->unqualified_lookups())
+        FirstQualifierInScope == E->getFirstQualifierFoundInScope())
       return E;
 
-    return getDerived().RebuildCXXDependentScopeMemberExpr(
-        Base.get(), BaseType, E->isArrow(), E->getOperatorLoc(), QualifierLoc,
-        TemplateKWLoc, UnqualifiedLookups.pairs(), NameInfo,
-        /*TemplateArgs*/ nullptr);
+    return getDerived().RebuildCXXDependentScopeMemberExpr(Base.get(),
+                                                       BaseType,
+                                                       E->isArrow(),
+                                                       E->getOperatorLoc(),
+                                                       QualifierLoc,
+                                                       TemplateKWLoc,
+                                                       FirstQualifierInScope,
+                                                       NameInfo,
+                                                       /*TemplateArgs*/nullptr);
   }
 
   TemplateArgumentListInfo TransArgs(E->getLAngleLoc(), E->getRAngleLoc());
@@ -14793,9 +14847,15 @@ TreeTransform<Derived>::TransformCXXDependentScopeMemberExpr(
                                               TransArgs))
     return ExprError();
 
-  return getDerived().RebuildCXXDependentScopeMemberExpr(
-      Base.get(), BaseType, E->isArrow(), E->getOperatorLoc(), QualifierLoc,
-      TemplateKWLoc, UnqualifiedLookups.pairs(), NameInfo, &TransArgs);
+  return getDerived().RebuildCXXDependentScopeMemberExpr(Base.get(),
+                                                     BaseType,
+                                                     E->isArrow(),
+                                                     E->getOperatorLoc(),
+                                                     QualifierLoc,
+                                                     TemplateKWLoc,
+                                                     FirstQualifierInScope,
+                                                     NameInfo,
+                                                     &TransArgs);
 }
 
 template <typename Derived>
@@ -14856,11 +14916,11 @@ ExprResult TreeTransform<Derived>::TransformUnresolvedMemberExpr(
   // first-qualifier-in-scope here, just in case we had a dependent
   // base (and therefore couldn't do the check) and a
   // nested-name-qualifier (and therefore could do the lookup).
-  ArrayRef<DeclAccessPair> UnqualifiedLookups;
+  NamedDecl *FirstQualifierInScope = nullptr;
 
   return getDerived().RebuildUnresolvedMemberExpr(
       Base.get(), BaseType, Old->getOperatorLoc(), Old->isArrow(), QualifierLoc,
-      TemplateKWLoc, UnqualifiedLookups, R,
+      TemplateKWLoc, FirstQualifierInScope, R,
       (Old->hasExplicitTemplateArgs() ? &TransArgs : nullptr));
 }
 
@@ -16217,18 +16277,22 @@ TreeTransform<Derived>::RebuildTemplateName(CXXScopeSpec &SS,
                                                   TemplateName(Template));
 }
 
-template <typename Derived>
-TemplateName TreeTransform<Derived>::RebuildTemplateName(
-    CXXScopeSpec &SS, SourceLocation TemplateKWLoc, const IdentifierInfo &Name,
-    SourceLocation NameLoc, QualType ObjectType, bool AllowInjectedClassName,
-    bool MayBeNNS) {
+template<typename Derived>
+TemplateName
+TreeTransform<Derived>::RebuildTemplateName(CXXScopeSpec &SS,
+                                            SourceLocation TemplateKWLoc,
+                                            const IdentifierInfo &Name,
+                                            SourceLocation NameLoc,
+                                            QualType ObjectType,
+                                            NamedDecl *FirstQualifierInScope,
+                                            bool AllowInjectedClassName) {
   UnqualifiedId TemplateName;
   TemplateName.setIdentifier(&Name, NameLoc);
   Sema::TemplateTy Template;
   getSema().ActOnTemplateName(/*Scope=*/nullptr, SS, TemplateKWLoc,
                               TemplateName, ParsedType::make(ObjectType),
                               /*EnteringContext=*/false, Template,
-                              AllowInjectedClassName, MayBeNNS);
+                              AllowInjectedClassName);
   return Template.get();
 }
 
@@ -16376,10 +16440,13 @@ TreeTransform<Derived>::RebuildCXXPseudoDestructorExpr(Expr *Base,
   }
 
   SourceLocation TemplateKWLoc; // FIXME: retrieve it from caller.
-  return getSema().BuildMemberReferenceExpr(
-      Base, BaseType, OperatorLoc, isArrow, SS, TemplateKWLoc, NameInfo,
-      /*TemplateArgs=*/nullptr,
-      /*S=*/nullptr);
+  return getSema().BuildMemberReferenceExpr(Base, BaseType,
+                                            OperatorLoc, isArrow,
+                                            SS, TemplateKWLoc,
+                                            /*FIXME: FirstQualifier*/ nullptr,
+                                            NameInfo,
+                                            /*TemplateArgs*/ nullptr,
+                                            /*S*/nullptr);
 }
 
 template<typename Derived>

diff  --git a/clang/lib/Serialization/ASTReaderStmt.cpp b/clang/lib/Serialization/ASTReaderStmt.cpp
index 6ccb4b01a036a..37f5c7f2bf20b 100644
--- a/clang/lib/Serialization/ASTReaderStmt.cpp
+++ b/clang/lib/Serialization/ASTReaderStmt.cpp
@@ -1992,43 +1992,42 @@ void ASTStmtReader::VisitCXXDependentScopeMemberExpr(
     CXXDependentScopeMemberExpr *E) {
   VisitExpr(E);
 
-  CurrentUnpackingBits.emplace(Record.readInt());
-  bool HasQualifier = CurrentUnpackingBits->getNextBit();
-  bool HasTemplateInfo = CurrentUnpackingBits->getNextBit();
-  unsigned NumUnqualifiedLookups = Record.readInt();
   unsigned NumTemplateArgs = Record.readInt();
-  E->CXXDependentScopeMemberExprBits.HasQualifier = HasQualifier;
-  E->CXXDependentScopeMemberExprBits.NumUnqualifiedLookups =
-      NumUnqualifiedLookups;
-  E->CXXDependentScopeMemberExprBits.HasTemplateKWAndArgsInfo = HasTemplateInfo;
+  CurrentUnpackingBits.emplace(Record.readInt());
+  bool HasTemplateKWAndArgsInfo = CurrentUnpackingBits->getNextBit();
+  bool HasFirstQualifierFoundInScope = CurrentUnpackingBits->getNextBit();
+
+  assert((HasTemplateKWAndArgsInfo == E->hasTemplateKWAndArgsInfo()) &&
+         "Wrong HasTemplateKWAndArgsInfo!");
+  assert(
+      (HasFirstQualifierFoundInScope == E->hasFirstQualifierFoundInScope()) &&
+      "Wrong HasFirstQualifierFoundInScope!");
+
+  if (HasTemplateKWAndArgsInfo)
+    ReadTemplateKWAndArgsInfo(
+        *E->getTrailingObjects<ASTTemplateKWAndArgsInfo>(),
+        E->getTrailingObjects<TemplateArgumentLoc>(), NumTemplateArgs);
+
+  assert((NumTemplateArgs == E->getNumTemplateArgs()) &&
+         "Wrong NumTemplateArgs!");
 
-  E->BaseType = Record.readType();
   E->CXXDependentScopeMemberExprBits.IsArrow =
       CurrentUnpackingBits->getNextBit();
 
+  E->BaseType = Record.readType();
+  E->QualifierLoc = Record.readNestedNameSpecifierLoc();
+  // not ImplicitAccess
   if (CurrentUnpackingBits->getNextBit())
     E->Base = Record.readSubExpr();
   else
     E->Base = nullptr;
 
-  E->OperatorLoc = Record.readSourceLocation();
-  E->MemberNameInfo = Record.readDeclarationNameInfo();
+  E->CXXDependentScopeMemberExprBits.OperatorLoc = readSourceLocation();
 
-  if (HasQualifier)
-    new (E->getTrailingObjects<NestedNameSpecifierLoc>())
-        NestedNameSpecifierLoc(Record.readNestedNameSpecifierLoc());
-
-  for (unsigned I = 0; I != NumUnqualifiedLookups; ++I) {
-    auto *FoundD = Record.readDeclAs<NamedDecl>();
-    auto AS = (AccessSpecifier)Record.readInt();
-    E->getTrailingObjects<DeclAccessPair>()[I] =
-        DeclAccessPair::make(FoundD, AS);
-  }
+  if (HasFirstQualifierFoundInScope)
+    *E->getTrailingObjects<NamedDecl *>() = readDeclAs<NamedDecl>();
 
-  if (HasTemplateInfo)
-    ReadTemplateKWAndArgsInfo(
-        *E->getTrailingObjects<ASTTemplateKWAndArgsInfo>(),
-        E->getTrailingObjects<TemplateArgumentLoc>(), NumTemplateArgs);
+  E->MemberNameInfo = Record.readDeclarationNameInfo();
 }
 
 void
@@ -4075,16 +4074,16 @@ Stmt *ASTReader::ReadStmtFromStream(ModuleFile &F) {
       break;
 
     case EXPR_CXX_DEPENDENT_SCOPE_MEMBER: {
+      unsigned NumTemplateArgs = Record[ASTStmtReader::NumExprFields];
       BitsUnpacker DependentScopeMemberBits(
-          Record[ASTStmtReader::NumExprFields]);
-      bool HasQualifier = DependentScopeMemberBits.getNextBit();
-      bool HasTemplateInfo = DependentScopeMemberBits.getNextBit();
-      unsigned NumUnqualifiedLookups = Record[ASTStmtReader::NumExprFields + 1];
-      unsigned NumTemplateArgs = Record[ASTStmtReader::NumExprFields + 2];
+          Record[ASTStmtReader::NumExprFields + 1]);
+      bool HasTemplateKWAndArgsInfo = DependentScopeMemberBits.getNextBit();
 
+      bool HasFirstQualifierFoundInScope =
+          DependentScopeMemberBits.getNextBit();
       S = CXXDependentScopeMemberExpr::CreateEmpty(
-          Context, HasQualifier, NumUnqualifiedLookups, HasTemplateInfo,
-          NumTemplateArgs);
+          Context, HasTemplateKWAndArgsInfo, NumTemplateArgs,
+          HasFirstQualifierFoundInScope);
       break;
     }
 

diff  --git a/clang/lib/Serialization/ASTWriterStmt.cpp b/clang/lib/Serialization/ASTWriterStmt.cpp
index 98606bbf8c4a0..d36f43fdaf262 100644
--- a/clang/lib/Serialization/ASTWriterStmt.cpp
+++ b/clang/lib/Serialization/ASTWriterStmt.cpp
@@ -1986,41 +1986,34 @@ void ASTStmtWriter::VisitCXXDependentScopeMemberExpr(
     CXXDependentScopeMemberExpr *E) {
   VisitExpr(E);
 
-  bool HasQualifier = E->hasQualifier();
-  unsigned NumUnqualifiedLookups = E->getNumUnqualifiedLookups();
-  bool HasTemplateInfo = E->hasTemplateKWAndArgsInfo();
-  unsigned NumTemplateArgs = E->getNumTemplateArgs();
-
-  // Write these first for easy access when deserializing, as they affect the
-  // size of the CXXDependentScopeMemberExpr.
+  // Don't emit anything here (or if you do you will have to update
+  // the corresponding deserialization function).
+  Record.push_back(E->getNumTemplateArgs());
   CurrentPackingBits.updateBits();
-  CurrentPackingBits.addBit(HasQualifier);
-  CurrentPackingBits.addBit(HasTemplateInfo);
-  Record.push_back(NumUnqualifiedLookups);
-  Record.push_back(NumTemplateArgs);
+  CurrentPackingBits.addBit(E->hasTemplateKWAndArgsInfo());
+  CurrentPackingBits.addBit(E->hasFirstQualifierFoundInScope());
+
+  if (E->hasTemplateKWAndArgsInfo()) {
+    const ASTTemplateKWAndArgsInfo &ArgInfo =
+        *E->getTrailingObjects<ASTTemplateKWAndArgsInfo>();
+    AddTemplateKWAndArgsInfo(ArgInfo,
+                             E->getTrailingObjects<TemplateArgumentLoc>());
+  }
 
-  Record.AddTypeRef(E->getBaseType());
   CurrentPackingBits.addBit(E->isArrow());
+
+  Record.AddTypeRef(E->getBaseType());
+  Record.AddNestedNameSpecifierLoc(E->getQualifierLoc());
   CurrentPackingBits.addBit(!E->isImplicitAccess());
   if (!E->isImplicitAccess())
     Record.AddStmt(E->getBase());
 
   Record.AddSourceLocation(E->getOperatorLoc());
 
-  Record.AddDeclarationNameInfo(E->MemberNameInfo);
-
-  if (HasQualifier)
-    Record.AddNestedNameSpecifierLoc(E->getQualifierLoc());
-
-  for (DeclAccessPair D : E->unqualified_lookups()) {
-    Record.AddDeclRef(D.getDecl());
-    Record.push_back(D.getAccess());
-  }
-
-  if (HasTemplateInfo)
-    AddTemplateKWAndArgsInfo(*E->getTrailingObjects<ASTTemplateKWAndArgsInfo>(),
-                             E->getTrailingObjects<TemplateArgumentLoc>());
+  if (E->hasFirstQualifierFoundInScope())
+    Record.AddDeclRef(E->getFirstQualifierFoundInScope());
 
+  Record.AddDeclarationNameInfo(E->MemberNameInfo);
   Code = serialization::EXPR_CXX_DEPENDENT_SCOPE_MEMBER;
 }
 

diff  --git a/clang/test/CXX/basic/basic.lookup/basic.lookup.classref/p1-cxx11.cpp b/clang/test/CXX/basic/basic.lookup/basic.lookup.classref/p1-cxx11.cpp
index 11eb67fb4f159..1afea99e8895c 100644
--- a/clang/test/CXX/basic/basic.lookup/basic.lookup.classref/p1-cxx11.cpp
+++ b/clang/test/CXX/basic/basic.lookup/basic.lookup.classref/p1-cxx11.cpp
@@ -55,19 +55,15 @@ namespace PR11856 {
 
   template<typename T> T *end(T*);
 
-  struct X { };
-  struct Y {
-    int end;
-  };
+  class X { };
   template <typename T>
   void Foo2() {
     T it1;
-    if (it1->end < it1->end) { }
+    if (it1->end < it1->end) {
+    }
 
     X *x;
-    if (x->end < 7) { } // expected-error{{no member named 'end' in 'PR11856::X'}}
-
-    Y *y;
-    if (y->end < 7) { }
+    if (x->end < 7) {  // expected-error{{no member named 'end' in 'PR11856::X'}}
+    }
   }
 }

diff  --git a/clang/test/CXX/basic/basic.lookup/basic.lookup.classref/p1.cpp b/clang/test/CXX/basic/basic.lookup/basic.lookup.classref/p1.cpp
index 5221b883f046c..e3599db18350b 100644
--- a/clang/test/CXX/basic/basic.lookup/basic.lookup.classref/p1.cpp
+++ b/clang/test/CXX/basic/basic.lookup/basic.lookup.classref/p1.cpp
@@ -86,19 +86,15 @@ namespace PR11856 {
 
   template<typename T> T *end(T*);
 
-  struct X { };
-  struct Y {
-    int end;
-  };
+  class X { };
   template <typename T>
   void Foo2() {
     T it1;
-    if (it1->end < it1->end) { }
+    if (it1->end < it1->end) {
+    }
 
     X *x;
-    if (x->end < 7) { } // expected-error{{no member named 'end' in 'PR11856::X'}}
-
-    Y *y;
-    if (y->end < 7) { }
+    if (x->end < 7) {  // expected-error{{no member named 'end' in 'PR11856::X'}}
+    }
   }
 }

diff  --git a/clang/test/CXX/basic/basic.lookup/basic.lookup.qual/basic.lookup.qual.general/p3-example3.cpp b/clang/test/CXX/basic/basic.lookup/basic.lookup.qual/basic.lookup.qual.general/p3-example3.cpp
deleted file mode 100644
index 423eacd21d441..0000000000000
--- a/clang/test/CXX/basic/basic.lookup/basic.lookup.qual/basic.lookup.qual.general/p3-example3.cpp
+++ /dev/null
@@ -1,27 +0,0 @@
-// RUN: %clang_cc1 -std=c++23 %s -verify
-
-int f();
-
-struct A {
-  int B, C; // expected-note {{declared as a non-template here}}
-  template<int> using D = void;
-  using T = void;
-  void f();
-};
-
-using B = A;
-template<int> using C = A;
-template<int> using D = A;
-template<int> using X = A;
-
-template<class T>
-void g(T *p) {
-  p->X<0>::f(); // expected-error {{no member named 'X' in 'A'}}
-  p->template X<0>::f();
-  p->B::f();
-  p->template C<0>::f(); // expected-error {{'C' following the 'template' keyword does not refer to a template}}
-  p->template D<0>::f(); // expected-error {{type 'template D<0>' (aka 'void') cannot be used prior to '::' because it has no members}}
-  p->T::f(); // expected-error {{'A::T' (aka 'void') is not a class, namespace, or enumeration}}
-}
-
-template void g(A*); // expected-note {{in instantiation of}}

diff  --git a/clang/test/CXX/basic/basic.lookup/basic.lookup.qual/basic.lookup.qual.general/p3.cpp b/clang/test/CXX/basic/basic.lookup/basic.lookup.qual/basic.lookup.qual.general/p3.cpp
deleted file mode 100644
index 7d843649c3f30..0000000000000
--- a/clang/test/CXX/basic/basic.lookup/basic.lookup.qual/basic.lookup.qual.general/p3.cpp
+++ /dev/null
@@ -1,98 +0,0 @@
-// RUN: %clang_cc1 -std=c++23 -Wno-unused %s -verify
-
-namespace Unambiguous {
-  struct A {
-    int x;
-
-    template<typename T>
-    using C = A;
-  };
-
-  using B = A;
-
-  template<typename T>
-  using D = A;
-
-  using E = void;
-
-  struct F : A {
-    void non_template() {
-      this->x;
-      this->A::x;
-      this->B::x;
-      this->C<int>::x;
-      this->D<int>::x;
-      this->E::x; // expected-error {{'Unambiguous::E' (aka 'void') is not a class, namespace, or enumeration}}
-    }
-  };
-
-  template<typename T>
-  void not_instantiated(T t) {
-    t.x;
-    t.A::x;
-    t.B::x;
-    t.C<int>::x; // expected-warning {{use 'template' keyword to treat 'C' as a dependent template name}}
-    t.template C<int>::x;
-    t.D<int>::x; // expected-warning {{use 'template' keyword to treat 'D' as a dependent template name}}
-    t.template D<int>::x;
-    t.E::x;
-  }
-
-  template<typename T>
-  void instantiated_valid(T t) {
-    t.x;
-    t.A::x;
-    t.B::x;
-    t.template C<int>::x;
-    t.template D<int>::x;
-    t.E::x;
-  }
-
-  template<typename T>
-  void instantiated_invalid(T t) {
-    t.x;
-    t.A::x;
-    t.B::x; // expected-error {{'Unambiguous::Invalid::B' (aka 'void') is not a class, namespace, or enumeration}}
-    t.template C<int>::x;
-    t.template D<int>::x; // expected-error {{'D' following the 'template' keyword does not refer to a template}}
-    t.E::x; // expected-error {{'Unambiguous::E' (aka 'void') is not a class, namespace, or enumeration}}
-  }
-
-  struct Valid : A {
-    using E = A;
-  };
-
-  template void instantiated_valid(Valid);
-
-  struct Invalid : A {
-    using B = void;
-    using D = A; // expected-note {{declared as a non-template here}}
-  };
-
-  template void instantiated_invalid(Invalid); // expected-note {{in instantiation of}}
-} // namespace Unambiguous
-
-namespace Ambiguous {
-  inline namespace N {
-    struct A { }; // expected-note {{candidate found by name lookup is 'Ambiguous::N::A'}}
-  }
-
-  struct A { }; // expected-note {{candidate found by name lookup is 'Ambiguous::A'}}
-
-  template<typename T>
-  void f(T t) {
-    t.A::x; // expected-error {{reference to 'A' is ambiguous}}
-  }
-
-  struct B {
-    using A = B;
-
-    int x;
-  };
-
-  struct C { };
-
-  template void f(B);
-  template void f(C); // expected-note {{in instantiation of}}
-
-} // namespace Ambiguous

diff  --git a/clang/test/CXX/class.derived/class.member.lookup/p8.cpp b/clang/test/CXX/class.derived/class.member.lookup/p8.cpp
index 97d3587881bbc..78e83c0ab4566 100644
--- a/clang/test/CXX/class.derived/class.member.lookup/p8.cpp
+++ b/clang/test/CXX/class.derived/class.member.lookup/p8.cpp
@@ -47,8 +47,8 @@ template<typename T>
 void DerivedT<T>::Inner() {
   Derived1T<T>::Foo();
   Derived2T<T>::Member = 42;
-  this->Derived1T<T>::Foo(); // expected-warning{{use 'template' keyword to treat 'Derived1T' as a dependent template name}}
-  this->Derived2T<T>::Member = 42; // expected-warning{{use 'template' keyword to treat 'Derived2T' as a dependent template name}}
+  this->Derived1T<T>::Foo();
+  this->Derived2T<T>::Member = 42;
   this->Foo(); // expected-error{{non-static member 'Foo' found in multiple base-class subobjects of type 'BaseT<int>'}}
 }
 

diff  --git a/clang/test/CXX/drs/cwg1xx.cpp b/clang/test/CXX/drs/cwg1xx.cpp
index 6bca460818425..e7dddd1ea9278 100644
--- a/clang/test/CXX/drs/cwg1xx.cpp
+++ b/clang/test/CXX/drs/cwg1xx.cpp
@@ -615,8 +615,10 @@ namespace cwg141 { // cwg141: 3.1
     //   cxx98-note@#cwg141-S {{lookup from the current scope refers here}}
     // expected-error@#cwg141-a {{no member named 'n' in 'cwg141::A::S<int>'; did you mean '::cwg141::S<int>::n'?}}
     //   expected-note@#cwg141-S {{'::cwg141::S<int>::n' declared here}}
+    // FIXME: we issue a useful diagnostic first, then some bogus ones.
     b.f<int>();
     // expected-error at -1 {{no member named 'f' in 'cwg141::B'}}
+    // expected-error at -2 +{{}}
     (void)b.S<int>::n;
   }
   template<typename T> struct C {
@@ -626,12 +628,10 @@ namespace cwg141 { // cwg141: 3.1
       // expected-error at -1 {{use 'template' keyword to treat 'f' as a dependent template name}}
     }
     void h() {
-      (void)t.S<int>::n;
-      // expected-error at -1 {{use 'template' keyword to treat 'S' as a dependent template name}}
+      (void)t.S<int>::n; // ok
     }
     void i() {
-      (void)t.S<int>();
-      // expected-error at -1 {{use 'template' keyword to treat 'S' as a dependent template name}}
+      (void)t.S<int>(); // ok!
     }
   };
   void h() { C<B>().h(); } // ok

diff  --git a/clang/test/CXX/temp/temp.names/p3-23.cpp b/clang/test/CXX/temp/temp.names/p3-23.cpp
deleted file mode 100644
index 27c24e1d61706..0000000000000
--- a/clang/test/CXX/temp/temp.names/p3-23.cpp
+++ /dev/null
@@ -1,237 +0,0 @@
-// RUN: %clang_cc1 -std=c++23 -Wno-unused %s -verify
-
-namespace FoundNothing {
-  template<typename T>
-  void f0(T &t) {
-    t.x<0;
-    t.x<0>; // expected-error {{expected expression}}
-    t.x<0>1;
-  }
-
-  template<typename T>
-  struct A {
-    void f1() {
-      this->x<0; // expected-error {{no member named 'x' in 'A<T>'}}
-      this->x<0>; // expected-error {{no member named 'x' in 'A<T>'}}
-                  // expected-error at -1 {{expected expression}}
-      this->x<0>1; // expected-error {{no member named 'x' in 'A<T>'}}
-    }
-  };
-} // namespace FoundNothing
-
-namespace FoundSingleNonTemplate {
-  void f0();
-
-  struct A0;
-
-  template<typename T>
-  void g0(T &t) {
-    t.f0<0;
-    t.f0<0>; // expected-error {{expected expression}}
-    t.f0<0>1;
-
-    t.A0<0;
-    t.A0<0>; // expected-error {{expected expression}}
-    t.A0<0>1;
-  }
-
-  template<typename T>
-  struct B {
-    void f1();
-
-    struct A1; // expected-note 3{{member 'A1' declared here}}
-
-    void g1() {
-      this->f0<0; // expected-error {{no member named 'f0' in 'B<T>'}}
-      this->f0<0>; // expected-error {{no member named 'f0' in 'B<T>'}}
-                   // expected-error at -1 {{expected expression}}
-      this->f0<0>1; // expected-error {{no member named 'f0' in 'B<T>'}}
-
-      this->A0<0; // expected-error {{no member named 'A0' in 'B<T>'}}
-      this->A0<0>; // expected-error {{no member named 'A0' in 'B<T>'}}
-                   // expected-error at -1 {{expected expression}}
-      this->A0<0>1; // expected-error {{no member named 'A0' in 'B<T>'}}
-
-      this->f1<0; // expected-error {{reference to non-static member function must be called}}
-      this->f1<0>; // expected-error {{reference to non-static member function must be called}}
-                   // expected-error at -1 {{expected expression}}
-      this->f1<0>1; // expected-error {{reference to non-static member function must be called}}
-
-      this->A1<0; // expected-error {{cannot refer to type member 'A1' in 'B<T>' with '->'}}
-      this->A1<0>; // expected-error {{cannot refer to type member 'A1' in 'B<T>' with '->'}}
-                   // expected-error at -1 {{expected expression}}
-      this->A1<0>1; // expected-error {{cannot refer to type member 'A1' in 'B<T>' with '->'}}
-    }
-  };
-} // namespace FoundSingleNonTemplate
-
-namespace FoundSingleTemplate {
-  template<int I>
-  void f0();
-
-  template<int I>
-  struct A0;
-
-  template<typename T>
-  void g0(T &t) {
-    t.f0<0;
-    t.f0<0>; // expected-error {{expected expression}}
-    t.f0<0>1;
-
-    t.A0<0;
-    t.A0<0>; // expected-error {{expected expression}}
-    t.A0<0>1;
-  }
-
-  template<typename T>
-  struct B {
-    template<int I>
-    void f1(); // expected-note 2{{possible target for call}}
-
-    template<int I>
-    struct A1; // expected-note 2{{member 'A1' declared here}}
-
-    void g1() {
-      this->f0<0; // expected-error {{no member named 'f0' in 'B<T>'}}
-      this->f0<0>; // expected-error {{no member named 'f0' in 'B<T>'}}
-      this->f0<0>1; // expected-error {{no member named 'f0' in 'B<T>'}}
-                    // expected-error at -1 {{expected ';' after expression}}
-
-      this->A0<0; // expected-error {{no member named 'A0' in 'B<T>'}}
-      this->A0<0>; // expected-error {{no member named 'A0' in 'B<T>'}}
-      this->A0<0>1; // expected-error {{no member named 'A0' in 'B<T>'}}
-                    // expected-error at -1 {{expected ';' after expression}}
-
-
-      this->f1<0; // expected-error {{expected '>'}}
-                  // expected-note at -1 {{to match this '<'}}
-      this->f1<0>; // expected-error {{reference to non-static member function must be called}}
-      this->f1<0>1; // expected-error {{reference to non-static member function must be called}}
-                    // expected-error at -1 {{expected ';' after expression}}
-
-      this->A1<0; // expected-error {{expected '>'}}
-                  // expected-note at -1 {{to match this '<'}}
-      this->A1<0>; // expected-error {{cannot refer to member 'A1' in 'B<T>' with '->'}}
-      this->A1<0>1; // expected-error {{cannot refer to member 'A1' in 'B<T>' with '->'}}
-                    // expected-error at -1 {{expected ';' after expression}}
-    }
-  };
-} // namespace FoundSingleTemplate
-
-namespace FoundAmbiguousNonTemplate {
-  inline namespace N {
-    int f0;
-
-    struct A0;
-  } // namespace N
-
-  void f0();
-
-  struct A0;
-
-  template<typename T>
-  void g0(T &t) {
-    t.f0<0;
-    t.f0<0>; // expected-error {{expected expression}}
-    t.f0<0>1;
-
-    t.A0<0;
-    t.A0<0>; // expected-error {{expected expression}}
-    t.A0<0>1;
-  }
-
-  template<typename T>
-  struct B {
-    void f1();
-
-    struct A1; // expected-note 3{{member 'A1' declared here}}
-
-    void g1() {
-      this->f0<0; // expected-error {{no member named 'f0' in 'B<T>'}}
-      this->f0<0>; // expected-error {{no member named 'f0' in 'B<T>'}}
-                   // expected-error at -1 {{expected expression}}
-      this->f0<0>1; // expected-error {{no member named 'f0' in 'B<T>'}}
-
-      this->A0<0; // expected-error {{no member named 'A0' in 'B<T>'}}
-      this->A0<0>; // expected-error {{no member named 'A0' in 'B<T>'}}
-                   // expected-error at -1 {{expected expression}}
-      this->A0<0>1; // expected-error {{no member named 'A0' in 'B<T>'}}
-
-      this->f1<0; // expected-error {{reference to non-static member function must be called}}
-      this->f1<0>; // expected-error {{reference to non-static member function must be called}}
-                   // expected-error at -1 {{expected expression}}
-      this->f1<0>1; // expected-error {{reference to non-static member function must be called}}
-
-      this->A1<0; // expected-error {{cannot refer to type member 'A1' in 'B<T>' with '->'}}
-      this->A1<0>; // expected-error {{cannot refer to type member 'A1' in 'B<T>' with '->'}}
-                   // expected-error at -1 {{expected expression}}
-      this->A1<0>1; // expected-error {{cannot refer to type member 'A1' in 'B<T>' with '->'}}
-    }
-  };
-} // namespace FoundAmbiguousNonTemplates
-
-namespace FoundAmbiguousTemplate {
-  inline namespace N {
-    template<int I>
-    int f0; // expected-note 3{{candidate found by name lookup is 'FoundAmbiguousTemplate::N::f0'}}
-
-    template<int I>
-    struct A0; // expected-note 3{{candidate found by name lookup is 'FoundAmbiguousTemplate::N::A0'}}
-  } // namespace N
-
-  template<int I>
-  void f0(); // expected-note 3{{candidate found by name lookup is 'FoundAmbiguousTemplate::f0'}}
-
-  template<int I>
-  struct A0; // expected-note 3{{candidate found by name lookup is 'FoundAmbiguousTemplate::A0'}}
-
-  template<typename T>
-  void g0(T &t) {
-    t.f0<0;
-    t.f0<0>; // expected-error {{expected expression}}
-    t.f0<0>1;
-
-    t.A0<0;
-    t.A0<0>; // expected-error {{expected expression}}
-    t.A0<0>1;
-  }
-
-  template<typename T>
-  struct B {
-    template<int I>
-    void f1(); // expected-note 2{{possible target for call}}
-
-    template<int I>
-    struct A1; // expected-note 2{{member 'A1' declared here}}
-
-    void g1() {
-      this->f0<0; // expected-error {{no member named 'f0' in 'B<T>'}}
-                  // expected-error at -1 {{reference to 'f0' is ambiguous}}
-      this->f0<0>; // expected-error {{no member named 'f0' in 'B<T>'}}
-                   // expected-error at -1 {{reference to 'f0' is ambiguous}}
-      this->f0<0>1; // expected-error {{no member named 'f0' in 'B<T>'}}
-                    // expected-error at -1 {{expected ';' after expression}}
-                    // expected-error at -2 {{reference to 'f0' is ambiguous}}
-
-      this->A0<0; // expected-error {{no member named 'A0' in 'B<T>'}}
-                  // expected-error at -1 {{reference to 'A0' is ambiguous}}
-      this->A0<0>; // expected-error {{no member named 'A0' in 'B<T>'}}
-                   // expected-error at -1 {{reference to 'A0' is ambiguous}}
-      this->A0<0>1; // expected-error {{no member named 'A0' in 'B<T>'}}
-                    // expected-error at -1 {{expected ';' after expression}}
-                    // expected-error at -2 {{reference to 'A0' is ambiguous}}
-
-      this->f1<0; // expected-error {{expected '>'}}
-                  // expected-note at -1 {{to match this '<'}}
-      this->f1<0>; // expected-error {{reference to non-static member function must be called}}
-      this->f1<0>1; // expected-error {{reference to non-static member function must be called}}
-                    // expected-error at -1 {{expected ';' after expression}}
-
-      this->A1<0; // expected-error {{expected '>'}}
-                  // expected-note at -1 {{to match this '<'}}
-      this->A1<0>; // expected-error {{cannot refer to member 'A1' in 'B<T>' with '->'}}
-      this->A1<0>1; // expected-error {{cannot refer to member 'A1' in 'B<T>' with '->'}}
-                    // expected-error at -1 {{expected ';' after expression}}
-    }
-  };
-} // namespace FoundAmbiguousTemplate

diff  --git a/clang/test/CXX/temp/temp.res/p3.cpp b/clang/test/CXX/temp/temp.res/p3.cpp
index a4d735e05e9b8..37ab93559e369 100644
--- a/clang/test/CXX/temp/temp.res/p3.cpp
+++ b/clang/test/CXX/temp/temp.res/p3.cpp
@@ -30,6 +30,6 @@ template<typename T> int A<T>::template C<int>::*f5() {} // expected-error {{has
 template<typename T> template<typename U> struct A<T>::B {
   friend A<T>::C<T> f6(); // ok, same as 'friend T f6();'
 
-  friend A<U>::C<T> f7(); // expected-warning {{use 'template' keyword to treat 'C' as a dependent template name}} expected-warning {{missing 'typename'}}
+  friend A<U>::C<T> f7(); // expected-error {{use 'template' keyword to treat 'C' as a dependent template name}} expected-warning {{missing 'typename'}}
   friend A<U>::template C<T> f8(); // expected-warning {{missing 'typename'}}
 };

diff  --git a/clang/test/FixIt/fixit.cpp b/clang/test/FixIt/fixit.cpp
index 144eefb3ae4bd..605c2d0bd0235 100644
--- a/clang/test/FixIt/fixit.cpp
+++ b/clang/test/FixIt/fixit.cpp
@@ -158,12 +158,12 @@ class F1 {
  
 template<class T>
 class F2  {
-  typename F1<T>:: /*template*/  Iterator<0> Mypos; // expected-warning {{use 'template' keyword to treat 'Iterator' as a dependent template name}}
+  typename F1<T>:: /*template*/  Iterator<0> Mypos; // expected-error {{use 'template' keyword to treat 'Iterator' as a dependent template name}}
 };
 
 template <class T>
 void f(){
-  typename F1<T>:: /*template*/ Iterator<0> Mypos; // expected-warning {{use 'template' keyword to treat 'Iterator' as a dependent template name}}
+  typename F1<T>:: /*template*/ Iterator<0> Mypos; // expected-error {{use 'template' keyword to treat 'Iterator' as a dependent template name}}
 }
 
 // Tests for &/* fixits

diff  --git a/clang/test/Misc/warning-flags.c b/clang/test/Misc/warning-flags.c
index 7b993f6849363..cdbe1e95cba96 100644
--- a/clang/test/Misc/warning-flags.c
+++ b/clang/test/Misc/warning-flags.c
@@ -18,7 +18,7 @@ This test serves two purposes:
 
 The list of warnings below should NEVER grow.  It should gradually shrink to 0.
 
-CHECK: Warnings without flags (64):
+CHECK: Warnings without flags (65):
 
 CHECK-NEXT:   ext_expected_semi_decl_list
 CHECK-NEXT:   ext_missing_whitespace_after_macro_name
@@ -61,6 +61,7 @@ CHECK-NEXT:   warn_invalid_cpu_supports
 CHECK-NEXT:   warn_maynot_respond
 CHECK-NEXT:   warn_method_param_redefinition
 CHECK-NEXT:   warn_missing_case_for_condition
+CHECK-NEXT:   warn_missing_dependent_template_keyword
 CHECK-NEXT:   warn_missing_whitespace_after_macro_name
 CHECK-NEXT:   warn_mt_message
 CHECK-NEXT:   warn_no_constructor_for_refconst

diff  --git a/clang/test/Parser/cxx2a-concepts-requires-expr.cpp b/clang/test/Parser/cxx2a-concepts-requires-expr.cpp
index 0c7f453b5c48d..5755844a323d2 100644
--- a/clang/test/Parser/cxx2a-concepts-requires-expr.cpp
+++ b/clang/test/Parser/cxx2a-concepts-requires-expr.cpp
@@ -78,7 +78,7 @@ bool r22 = requires { typename s::~s; };
 
 template<typename T>
 bool r23 = requires { typename identity<T>::temp<T>; };
-// expected-warning at -1 {{use 'template' keyword to treat 'temp' as a dependent template name}}
+// expected-error at -1 {{use 'template' keyword to treat 'temp' as a dependent template name}}
 
 template<typename T>
 bool r24 = requires {

diff  --git a/clang/test/SemaCXX/cxx0x-noexcept-expression.cpp b/clang/test/SemaCXX/cxx0x-noexcept-expression.cpp
index a01edc77e02af..b3c102830f359 100644
--- a/clang/test/SemaCXX/cxx0x-noexcept-expression.cpp
+++ b/clang/test/SemaCXX/cxx0x-noexcept-expression.cpp
@@ -127,7 +127,7 @@ void f1() {
   // `dependent` should be type-dependent because the noexcept-expression should be value-dependent
   // (it is true if T is int*, false if T is Polymorphic<false, false>* for example)
   dependent.f<void>();  // This should need to be `.template f` to parse as a template
-  // expected-warning at -1 {{use 'template' keyword to treat 'f' as a dependent template name}}
+  // expected-error at -1 {{use 'template' keyword to treat 'f' as a dependent template name}}
 }
 template<typename... T>
 void f2() {
@@ -135,14 +135,14 @@ void f2() {
   // X<true> when T...[0] is a type with some operator&& which returns int*
   // X<false> when sizeof...(T) == 0
   dependent.f<void>();
-  // expected-warning at -1 {{use 'template' keyword to treat 'f' as a dependent template name}}
+  // expected-error at -1 {{use 'template' keyword to treat 'f' as a dependent template name}}
 }
 template<typename T>
 void f3() {
   X<noexcept(typeid(*static_cast<T*>(nullptr)))> dependent;
   // X<true> when T is int, X<false> when T is Polymorphic<false, false>
   dependent.f<void>();
-  // expected-warning at -1 {{use 'template' keyword to treat 'f' as a dependent template name}}
+  // expected-error at -1 {{use 'template' keyword to treat 'f' as a dependent template name}}
 }
 template<typename T>
 void f4() {

diff  --git a/clang/test/SemaCXX/pseudo-destructors.cpp b/clang/test/SemaCXX/pseudo-destructors.cpp
index 44dc9ce8b1520..55a96002be2ab 100644
--- a/clang/test/SemaCXX/pseudo-destructors.cpp
+++ b/clang/test/SemaCXX/pseudo-destructors.cpp
@@ -22,21 +22,21 @@ void cv_test(const volatile T* cvt) {
 void f(A* a, Foo *f, int *i, double *d, int ii) {
   a->~A();
   a->A::~A();
-
+  
   a->~foo(); // expected-error{{undeclared identifier 'foo' in destructor name}}
-
+  
   a->~Bar(); // expected-error{{destructor type 'Bar' (aka 'Foo') in object destruction expression does not match the type 'A' of the object being destroyed}}
-
+  
   f->~Bar();
   f->~Foo();
   i->~Bar(); // expected-error{{does not match}}
-
+  
   g().~Bar(); // expected-error{{non-scalar}}
-
+  
   f->::~Bar(); // expected-error {{not a structure or union}}
   f->::Bar::~Bar();
   f->N::~Wibble(); // expected-error{{'N' does not refer to a type}} expected-error{{'Wibble' does not refer to a type}}
-
+  
   f->Bar::~Bar(17, 42); // expected-error{{cannot have any arguments}}
 
   i->~Integer();
@@ -148,12 +148,12 @@ namespace TwoPhaseLookup {
   namespace Template {
     template<typename T> struct Y {};
     template<class U> using G = Y<U>;
-    template<typename T> void f(T *p) { p->~G<int>(); } // expected-error {{no member named 'G'}}
+    template<typename T> void f(T *p) { p->~G<int>(); } // expected-error {{no member named '~Y'}}
     void h1(Y<int> *p) { p->~G<int>(); }
-    void h2(Y<int> *p) { f(p); } // expected-note {{instantiation of}}
+    void h2(Y<int> *p) { f(p); }
     namespace N { template<typename T> struct G {}; }
     void h3(N::G<int> *p) { p->~G<int>(); }
-    void h4(N::G<int> *p) { f(p); }
+    void h4(N::G<int> *p) { f(p); } // expected-note {{instantiation of}}
   }
 
   namespace TemplateUndeclared {

diff  --git a/clang/test/SemaCXX/static-assert-cxx17.cpp b/clang/test/SemaCXX/static-assert-cxx17.cpp
index 754f4ae5f1d38..41a7b025d0eb7 100644
--- a/clang/test/SemaCXX/static-assert-cxx17.cpp
+++ b/clang/test/SemaCXX/static-assert-cxx17.cpp
@@ -96,7 +96,7 @@ void foo6() {
   // expected-error at -1{{static assertion failed due to requirement 'static_cast<const X<int> *>(nullptr)'}}
   static_assert((const X<typename T::T>[]){} == nullptr);
   // expected-error at -1{{static assertion failed due to requirement '(const X<int>[0]){} == nullptr'}}
-  static_assert(sizeof(X<decltype(X<typename T::T>().template X<typename T::T>::~X())>) == 0);
+  static_assert(sizeof(X<decltype(X<typename T::T>().X<typename T::T>::~X())>) == 0);
   // expected-error at -1{{static assertion failed due to requirement 'sizeof(X<void>) == 0'}} \
   // expected-note at -1 {{evaluates to '8 == 0'}}
   static_assert(constexpr_return_false<typename T::T, typename T::U>());

diff  --git a/clang/test/SemaTemplate/dependent-base-classes.cpp b/clang/test/SemaTemplate/dependent-base-classes.cpp
index 4cb88a5b4070a..92a37efaa7e73 100644
--- a/clang/test/SemaTemplate/dependent-base-classes.cpp
+++ b/clang/test/SemaTemplate/dependent-base-classes.cpp
@@ -1,12 +1,12 @@
 // RUN: %clang_cc1 -fsyntax-only -verify %s
 
 template<typename T, typename U>
-struct X0 : T::template apply<U> {
+struct X0 : T::template apply<U> { 
   X0(U u) : T::template apply<U>(u) { }
 };
 
 template<typename T, typename U>
-struct X1 : T::apply<U> { }; // expected-warning{{use 'template' keyword to treat 'apply' as a dependent template name}}
+struct X1 : T::apply<U> { }; // expected-error{{use 'template' keyword to treat 'apply' as a dependent template name}}
 
 template<typename T>
 struct X2 : vector<T> { }; // expected-error{{no template named 'vector'}}
@@ -85,7 +85,7 @@ namespace PR6081 {
   struct A { };
 
   template<typename T>
-  class B : public A<T>
+  class B : public A<T> 
   {
   public:
     template< class X >
@@ -109,9 +109,9 @@ namespace PR6081 {
 
 namespace PR6413 {
   template <typename T> class Base_A { };
-
+  
   class Base_B { };
-
+  
   template <typename T>
   class Derived
     : public virtual Base_A<T>
@@ -120,12 +120,12 @@ namespace PR6413 {
 }
 
 namespace PR5812 {
-  template <class T> struct Base {
-    Base* p;
-  };
+  template <class T> struct Base { 
+    Base* p; 
+  }; 
 
-  template <class T> struct Derived: public Base<T> {
-    typename Derived::Base* p; // meaning Derived::Base<T>
+  template <class T> struct Derived: public Base<T> { 
+    typename Derived::Base* p; // meaning Derived::Base<T> 
   };
 
   Derived<int> di;

diff  --git a/clang/test/SemaTemplate/dependent-template-recover.cpp b/clang/test/SemaTemplate/dependent-template-recover.cpp
index c763989e6dadb..c7e27e8da25f1 100644
--- a/clang/test/SemaTemplate/dependent-template-recover.cpp
+++ b/clang/test/SemaTemplate/dependent-template-recover.cpp
@@ -2,15 +2,15 @@
 template<typename T, typename U, int N>
 struct X {
   void f(T* t) {
-    t->f0<U>(); // expected-warning{{use 'template' keyword to treat 'f0' as a dependent template name}}
-    t->f0<int>(); // expected-warning{{use 'template' keyword to treat 'f0' as a dependent template name}}
+    t->f0<U>(); // expected-error{{use 'template' keyword to treat 'f0' as a dependent template name}}
+    t->f0<int>(); // expected-error{{use 'template' keyword to treat 'f0' as a dependent template name}}
 
-    t->operator+<U const, 1>(1); // expected-warning{{use 'template' keyword to treat 'operator +' as a dependent template name}}
-    t->f1<int const, 2>(1); // expected-warning{{use 'template' keyword to treat 'f1' as a dependent template name}}
+    t->operator+<U const, 1>(1); // expected-error{{use 'template' keyword to treat 'operator +' as a dependent template name}}
+    t->f1<int const, 2>(1); // expected-error{{use 'template' keyword to treat 'f1' as a dependent template name}}
     t->f1<3, int const>(1); // expected-error{{missing 'template' keyword prior to dependent template name 'f1'}}
 
-    T::getAs<U>(); // expected-warning{{use 'template' keyword to treat 'getAs' as a dependent template name}}
-    t->T::getAs<U>(); // expected-warning{{use 'template' keyword to treat 'getAs' as a dependent template name}}
+    T::getAs<U>(); // expected-error{{use 'template' keyword to treat 'getAs' as a dependent template name}}
+    t->T::getAs<U>(); // expected-error{{use 'template' keyword to treat 'getAs' as a dependent template name}}
 
     (*t).f2<N>(); // expected-error{{missing 'template' keyword prior to dependent template name 'f2'}}
     (*t).f2<0>(); // expected-error{{missing 'template' keyword prior to dependent template name 'f2'}}

diff  --git a/clang/test/SemaTemplate/temp_arg_nontype_cxx20.cpp b/clang/test/SemaTemplate/temp_arg_nontype_cxx20.cpp
index 7768d2f03ac5b..ad73daa8e214c 100644
--- a/clang/test/SemaTemplate/temp_arg_nontype_cxx20.cpp
+++ b/clang/test/SemaTemplate/temp_arg_nontype_cxx20.cpp
@@ -115,7 +115,7 @@ namespace CopyCounting {
   static_assert(f(X<A{}>()) == 0);
 
   template<A a> struct Y { void f(); };
-  template<A a> void g(Y<a> y) { y.template Y<a>::f(); }
+  template<A a> void g(Y<a> y) { y.Y<a>::f(); }
   void h() { constexpr A a; g<a>(Y<a>{}); }
 
   template<A a> struct Z {

diff  --git a/clang/test/SemaTemplate/template-id-expr.cpp b/clang/test/SemaTemplate/template-id-expr.cpp
index 760d6c5852403..dc12823ae307f 100644
--- a/clang/test/SemaTemplate/template-id-expr.cpp
+++ b/clang/test/SemaTemplate/template-id-expr.cpp
@@ -19,7 +19,7 @@ template<typename T>
 struct X0 {
   template<typename U>
   void f1();
-
+  
   template<typename U>
   void f2(U) {
     f1<U>();
@@ -39,9 +39,9 @@ struct Y {
 template<int I>
 struct X {
   X(int, int);
-  void f() {
-    Y<X<I> >(X<I>(0, 0));
-    Y<X<I> >(::X<I>(0, 0));
+  void f() { 
+    Y<X<I> >(X<I>(0, 0)); 
+    Y<X<I> >(::X<I>(0, 0)); 
   }
 };
 
@@ -149,11 +149,11 @@ struct Y2 : Y1<T> {
 
     int x;
     x = Y1::f4(0);
-    x = Y1::f4<int>(0); // expected-warning {{use 'template'}} expected-error {{assigning to 'int' from incompatible type 'void'}}
+    x = Y1::f4<int>(0); // expected-error {{use 'template'}} expected-error {{assigning to 'int' from incompatible type 'void'}}
     x = Y1::template f4(0); // expected-error {{assigning to 'int' from incompatible type 'void'}} expected-error {{a template argument list is expected after a name prefixed by the template keyword}}
 
     x = p->f4(0);
-    x = p->f4<int>(0); // expected-error {{assigning to 'int' from incompatible type 'void'}} expected-warning {{use 'template'}}
+    x = p->f4<int>(0); // expected-error {{assigning to 'int' from incompatible type 'void'}} expected-error {{use 'template'}}
     x = p->template f4(0); // expected-error {{assigning to 'int' from incompatible type 'void'}} expected-error {{a template argument list is expected after a name prefixed by the template keyword}}
   }
 };
@@ -184,7 +184,7 @@ class E {
 #if __cplusplus <= 199711L
 // expected-warning at +2 {{extension}}
 #endif
-template<typename T> using D = int; // expected-note {{declared here}}
+template<typename T> using D = int; // expected-note {{declared here}} 
 E<D> ed; // expected-note {{instantiation of}}
 
 namespace non_functions {

diff  --git a/clang/test/SemaTemplate/typename-specifier-3.cpp b/clang/test/SemaTemplate/typename-specifier-3.cpp
index a9010969322e5..714830f0032d2 100644
--- a/clang/test/SemaTemplate/typename-specifier-3.cpp
+++ b/clang/test/SemaTemplate/typename-specifier-3.cpp
@@ -46,7 +46,7 @@ namespace PR12884_half_fixed {
       typedef int arg;
     };
     struct C {
-      typedef typename B::X<typename B::arg> x; // expected-warning {{use 'template'}} expected-error {{refers to non-type}}
+      typedef typename B::X<typename B::arg> x; // expected-error {{use 'template'}} expected-error {{refers to non-type}}
     };
   };
 

diff  --git a/libcxx/include/regex b/libcxx/include/regex
index 17ad0cf5b2aea..b814135121321 100644
--- a/libcxx/include/regex
+++ b/libcxx/include/regex
@@ -4214,7 +4214,7 @@ public:
   _LIBCPP_HIDE_FROM_ABI int compare(const value_type* __s) const { return str().compare(__s); }
 
   _LIBCPP_HIDE_FROM_ABI void swap(sub_match& __s) _NOEXCEPT_(__is_nothrow_swappable_v<_BidirectionalIterator>) {
-    this->template pair<_BidirectionalIterator, _BidirectionalIterator>::swap(__s);
+    this->pair<_BidirectionalIterator, _BidirectionalIterator>::swap(__s);
     std::swap(matched, __s.matched);
   }
 };

diff  --git a/llvm/include/llvm/ADT/ArrayRef.h b/llvm/include/llvm/ADT/ArrayRef.h
index 1c6799f1c56ed..ac40ec4a6b240 100644
--- a/llvm/include/llvm/ADT/ArrayRef.h
+++ b/llvm/include/llvm/ADT/ArrayRef.h
@@ -460,11 +460,8 @@ namespace llvm {
 
     OwningArrayRef &operator=(OwningArrayRef &&Other) {
       delete[] this->data();
-      using Base = MutableArrayRef<T>;
-      // GCC versions prior to 11.1 incorrectly reject if the 'template' keyword
-      // is used prior to the nested-name-specifier here.
-      this->Base::operator=(Other);
-      Other.Base::operator=(Base());
+      this->MutableArrayRef<T>::operator=(Other);
+      Other.MutableArrayRef<T>::operator=(MutableArrayRef<T>());
       return *this;
     }
 


        


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