[clang] Reapply "[Clang][Sema] Fix crash when 'this' is used in a dependent class scope function template specialization that instantiates to a static member function (#87541, #88311)" (PR #88731)

Krystian Stasiowski via cfe-commits cfe-commits at lists.llvm.org
Mon Apr 15 06:24:07 PDT 2024


https://github.com/sdkrystian created https://github.com/llvm/llvm-project/pull/88731

Reapplies #87541 and #88311 (again) addressing the bug which caused expressions naming overload sets to be incorrectly rebuilt, as well as the bug which caused base class members to always be treated as overload sets.

>From 4640d869aeb83a457b16f553de215e3d106eaa67 Mon Sep 17 00:00:00 2001
From: Krystian Stasiowski <sdkrystian at gmail.com>
Date: Mon, 15 Apr 2024 09:17:39 -0400
Subject: [PATCH] Reapply "[Clang][Sema] Fix crash when 'this' is used in a
 dependent class scope function template specialization that instantiates to a
 static member function (#87541, #88311)"

Reapplies #87541 and #88311 addressing the bug which caused expressions naming
overload sets to be incorrectly rebuilt, as well as the bug which caused
base class members to always be treated as overload sets.
---
 clang/docs/ReleaseNotes.rst                   |   2 +
 clang/include/clang/AST/ExprCXX.h             |   3 +-
 clang/include/clang/Sema/Sema.h               |  16 +-
 clang/lib/AST/ASTImporter.cpp                 |   2 +-
 clang/lib/AST/ExprCXX.cpp                     |   8 +-
 clang/lib/Sema/SemaCoroutine.cpp              |   4 +-
 clang/lib/Sema/SemaDecl.cpp                   |   2 +-
 clang/lib/Sema/SemaExpr.cpp                   |  30 +--
 clang/lib/Sema/SemaExprCXX.cpp                |  61 +++---
 clang/lib/Sema/SemaExprMember.cpp             |  63 ++++--
 clang/lib/Sema/SemaOpenMP.cpp                 |   6 +-
 clang/lib/Sema/SemaOverload.cpp               |   3 +-
 .../lib/Sema/SemaTemplateInstantiateDecl.cpp  |   8 +
 clang/lib/Sema/TreeTransform.h                |  75 ++++---
 .../SemaTemplate/instantiate-using-decl.cpp   |   2 +-
 ...ms-function-specialization-class-scope.cpp | 201 +++++++++++++++++-
 16 files changed, 371 insertions(+), 115 deletions(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index de5fa99bff5dbe..ade8f4e93d5a0c 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -529,6 +529,8 @@ Bug Fixes to C++ Support
 - Fix an issue caused by not handling invalid cases when substituting into the parameter mapping of a constraint. Fixes (#GH86757).
 - Fixed a bug that prevented member function templates of class templates declared with a deduced return type
   from being explicitly specialized for a given implicit instantiation of the class template.
+- Fixed a crash when ``this`` is used in a dependent class scope function template specialization
+  that instantiates to a static member function.
 
 - Fix crash when inheriting from a cv-qualified type. Fixes:
   (`#35603 <https://github.com/llvm/llvm-project/issues/35603>`_)
diff --git a/clang/include/clang/AST/ExprCXX.h b/clang/include/clang/AST/ExprCXX.h
index d28e5c3a78ee4b..4d5293566580ae 100644
--- a/clang/include/clang/AST/ExprCXX.h
+++ b/clang/include/clang/AST/ExprCXX.h
@@ -3219,7 +3219,8 @@ class UnresolvedLookupExpr final
   Create(const ASTContext &Context, CXXRecordDecl *NamingClass,
          NestedNameSpecifierLoc QualifierLoc,
          const DeclarationNameInfo &NameInfo, bool RequiresADL, bool Overloaded,
-         UnresolvedSetIterator Begin, UnresolvedSetIterator End);
+         UnresolvedSetIterator Begin, UnresolvedSetIterator End,
+         bool KnownDependent);
 
   // After canonicalization, there may be dependent template arguments in
   // CanonicalConverted But none of Args is dependent. When any of
diff --git a/clang/include/clang/Sema/Sema.h b/clang/include/clang/Sema/Sema.h
index c6035445e90192..c6e0332c3176b3 100644
--- a/clang/include/clang/Sema/Sema.h
+++ b/clang/include/clang/Sema/Sema.h
@@ -5452,7 +5452,8 @@ class Sema final : public SemaBase {
 
   ExprResult BuildDeclarationNameExpr(const CXXScopeSpec &SS, LookupResult &R,
                                       bool NeedsADL,
-                                      bool AcceptInvalidDecl = false);
+                                      bool AcceptInvalidDecl = false,
+                                      bool NeedUnresolved = false);
   ExprResult BuildDeclarationNameExpr(
       const CXXScopeSpec &SS, const DeclarationNameInfo &NameInfo, NamedDecl *D,
       NamedDecl *FoundD = nullptr,
@@ -6595,7 +6596,10 @@ class Sema final : public SemaBase {
                             SourceLocation RParenLoc);
 
   //// ActOnCXXThis -  Parse 'this' pointer.
-  ExprResult ActOnCXXThis(SourceLocation loc);
+  ExprResult ActOnCXXThis(SourceLocation Loc);
+
+  /// Check whether the type of 'this' is valid in the current context.
+  bool CheckCXXThisType(SourceLocation Loc, QualType Type);
 
   /// Build a CXXThisExpr and mark it referenced in the current context.
   Expr *BuildCXXThisExpr(SourceLocation Loc, QualType Type, bool IsImplicit);
@@ -7018,10 +7022,14 @@ class Sema final : public SemaBase {
   ///@{
 
 public:
+  /// Check whether an expression might be an implicit class member access.
+  bool isPotentialImplicitMemberAccess(const CXXScopeSpec &SS, LookupResult &R,
+                                       bool IsAddressOfOperand);
+
   ExprResult BuildPossibleImplicitMemberExpr(
       const CXXScopeSpec &SS, SourceLocation TemplateKWLoc, LookupResult &R,
-      const TemplateArgumentListInfo *TemplateArgs, const Scope *S,
-      UnresolvedLookupExpr *AsULE = nullptr);
+      const TemplateArgumentListInfo *TemplateArgs, const Scope *S);
+
   ExprResult
   BuildImplicitMemberExpr(const CXXScopeSpec &SS, SourceLocation TemplateKWLoc,
                           LookupResult &R,
diff --git a/clang/lib/AST/ASTImporter.cpp b/clang/lib/AST/ASTImporter.cpp
index 6aaa34c55ce307..0928e6cd2b37a8 100644
--- a/clang/lib/AST/ASTImporter.cpp
+++ b/clang/lib/AST/ASTImporter.cpp
@@ -8562,7 +8562,7 @@ ASTNodeImporter::VisitUnresolvedLookupExpr(UnresolvedLookupExpr *E) {
   return UnresolvedLookupExpr::Create(
       Importer.getToContext(), *ToNamingClassOrErr, *ToQualifierLocOrErr,
       ToNameInfo, E->requiresADL(), E->isOverloaded(), ToDecls.begin(),
-      ToDecls.end());
+      ToDecls.end(), /*KnownDependent=*/E->isTypeDependent());
 }
 
 ExpectedStmt
diff --git a/clang/lib/AST/ExprCXX.cpp b/clang/lib/AST/ExprCXX.cpp
index a581963188433e..7a20f0f80fa541 100644
--- a/clang/lib/AST/ExprCXX.cpp
+++ b/clang/lib/AST/ExprCXX.cpp
@@ -374,14 +374,16 @@ UnresolvedLookupExpr *UnresolvedLookupExpr::Create(
     const ASTContext &Context, CXXRecordDecl *NamingClass,
     NestedNameSpecifierLoc QualifierLoc, const DeclarationNameInfo &NameInfo,
     bool RequiresADL, bool Overloaded, UnresolvedSetIterator Begin,
-    UnresolvedSetIterator End) {
+    UnresolvedSetIterator End, bool KnownDependent) {
   unsigned NumResults = End - Begin;
   unsigned Size = totalSizeToAlloc<DeclAccessPair, ASTTemplateKWAndArgsInfo,
                                    TemplateArgumentLoc>(NumResults, 0, 0);
   void *Mem = Context.Allocate(Size, alignof(UnresolvedLookupExpr));
   return new (Mem) UnresolvedLookupExpr(Context, NamingClass, QualifierLoc,
-                                        SourceLocation(), NameInfo, RequiresADL,
-                                        Overloaded, nullptr, Begin, End, false);
+                                        /*TemplateKWLoc=*/SourceLocation(),
+                                        NameInfo, RequiresADL, Overloaded,
+                                        /*TemplateArgs=*/nullptr, Begin, End,
+                                        KnownDependent);
 }
 
 UnresolvedLookupExpr *UnresolvedLookupExpr::Create(
diff --git a/clang/lib/Sema/SemaCoroutine.cpp b/clang/lib/Sema/SemaCoroutine.cpp
index 736632857efc36..57b59e4f36f1ab 100644
--- a/clang/lib/Sema/SemaCoroutine.cpp
+++ b/clang/lib/Sema/SemaCoroutine.cpp
@@ -822,8 +822,8 @@ ExprResult Sema::BuildOperatorCoawaitLookupExpr(Scope *S, SourceLocation Loc) {
       (Functions.size() == 1 && isa<FunctionTemplateDecl>(*Functions.begin()));
   Expr *CoawaitOp = UnresolvedLookupExpr::Create(
       Context, /*NamingClass*/ nullptr, NestedNameSpecifierLoc(),
-      DeclarationNameInfo(OpName, Loc), /*RequiresADL*/ true, IsOverloaded,
-      Functions.begin(), Functions.end());
+      DeclarationNameInfo(OpName, Loc), /*RequiresADL*/true, IsOverloaded,
+      Functions.begin(), Functions.end(), /*KnownDependent=*/false);
   assert(CoawaitOp);
   return CoawaitOp;
 }
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 8b3b9d020db572..2844cc4f3b7f01 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -1240,7 +1240,7 @@ Sema::NameClassification Sema::ClassifyName(Scope *S, CXXScopeSpec &SS,
   return NameClassification::OverloadSet(UnresolvedLookupExpr::Create(
       Context, Result.getNamingClass(), SS.getWithLocInContext(Context),
       Result.getLookupNameInfo(), ADL, Result.isOverloadedResult(),
-      Result.begin(), Result.end()));
+      Result.begin(), Result.end(), /*KnownDependent=*/false));
 }
 
 ExprResult
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index c5395fb2068a18..9e52382252d8b6 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -2917,26 +2917,9 @@ Sema::ActOnIdExpression(Scope *S, CXXScopeSpec &SS,
   // to get this right here so that we don't end up making a
   // spuriously dependent expression if we're inside a dependent
   // instance method.
-  if (getLangOpts().CPlusPlus && !R.empty() &&
-      (*R.begin())->isCXXClassMember()) {
-    bool MightBeImplicitMember;
-    if (!IsAddressOfOperand)
-      MightBeImplicitMember = true;
-    else if (!SS.isEmpty())
-      MightBeImplicitMember = false;
-    else if (R.isOverloadedResult())
-      MightBeImplicitMember = false;
-    else if (R.isUnresolvableResult())
-      MightBeImplicitMember = true;
-    else
-      MightBeImplicitMember = isa<FieldDecl>(R.getFoundDecl()) ||
-                              isa<IndirectFieldDecl>(R.getFoundDecl()) ||
-                              isa<MSPropertyDecl>(R.getFoundDecl());
-
-    if (MightBeImplicitMember)
-      return BuildPossibleImplicitMemberExpr(SS, TemplateKWLoc,
-                                             R, TemplateArgs, S);
-  }
+  if (isPotentialImplicitMemberAccess(SS, R, IsAddressOfOperand))
+    return BuildPossibleImplicitMemberExpr(SS, TemplateKWLoc, R, TemplateArgs,
+                                           S);
 
   if (TemplateArgs || TemplateKWLoc.isValid()) {
 
@@ -3447,10 +3430,11 @@ static bool ShouldLookupResultBeMultiVersionOverload(const LookupResult &R) {
 
 ExprResult Sema::BuildDeclarationNameExpr(const CXXScopeSpec &SS,
                                           LookupResult &R, bool NeedsADL,
-                                          bool AcceptInvalidDecl) {
+                                          bool AcceptInvalidDecl,
+                                          bool NeedUnresolved) {
   // If this is a single, fully-resolved result and we don't need ADL,
   // just build an ordinary singleton decl ref.
-  if (!NeedsADL && R.isSingleResult() &&
+  if (!NeedUnresolved && !NeedsADL && R.isSingleResult() &&
       !R.getAsSingle<FunctionTemplateDecl>() &&
       !ShouldLookupResultBeMultiVersionOverload(R))
     return BuildDeclarationNameExpr(SS, R.getLookupNameInfo(), R.getFoundDecl(),
@@ -3475,7 +3459,7 @@ ExprResult Sema::BuildDeclarationNameExpr(const CXXScopeSpec &SS,
                                    SS.getWithLocInContext(Context),
                                    R.getLookupNameInfo(),
                                    NeedsADL, R.isOverloadedResult(),
-                                   R.begin(), R.end());
+                                   R.begin(), R.end(), NeedUnresolved);
 
   return ULE;
 }
diff --git a/clang/lib/Sema/SemaExprCXX.cpp b/clang/lib/Sema/SemaExprCXX.cpp
index fa7b92a43346b1..25f23a3abf1718 100644
--- a/clang/lib/Sema/SemaExprCXX.cpp
+++ b/clang/lib/Sema/SemaExprCXX.cpp
@@ -1416,26 +1416,42 @@ bool Sema::CheckCXXThisCapture(SourceLocation Loc, const bool Explicit,
 }
 
 ExprResult Sema::ActOnCXXThis(SourceLocation Loc) {
-  /// C++ 9.3.2: In the body of a non-static member function, the keyword this
-  /// is a non-lvalue expression whose value is the address of the object for
-  /// which the function is called.
+  // C++20 [expr.prim.this]p1:
+  //   The keyword this names a pointer to the object for which an
+  //   implicit object member function is invoked or a non-static
+  //   data member's initializer is evaluated.
   QualType ThisTy = getCurrentThisType();
 
-  if (ThisTy.isNull()) {
-    DeclContext *DC = getFunctionLevelDeclContext();
+  if (CheckCXXThisType(Loc, ThisTy))
+    return ExprError();
 
-    if (const auto *Method = dyn_cast<CXXMethodDecl>(DC);
-        Method && Method->isExplicitObjectMemberFunction()) {
-      return Diag(Loc, diag::err_invalid_this_use) << 1;
-    }
+  return BuildCXXThisExpr(Loc, ThisTy, /*IsImplicit=*/false);
+}
 
-    if (isLambdaCallWithExplicitObjectParameter(CurContext))
-      return Diag(Loc, diag::err_invalid_this_use) << 1;
+bool Sema::CheckCXXThisType(SourceLocation Loc, QualType Type) {
+  if (!Type.isNull())
+    return false;
 
-    return Diag(Loc, diag::err_invalid_this_use) << 0;
+  // C++20 [expr.prim.this]p3:
+  //   If a declaration declares a member function or member function template
+  //   of a class X, the expression this is a prvalue of type
+  //   "pointer to cv-qualifier-seq X" wherever X is the current class between
+  //   the optional cv-qualifier-seq and the end of the function-definition,
+  //   member-declarator, or declarator. It shall not appear within the
+  //   declaration of either a static member function or an explicit object
+  //   member function of the current class (although its type and value
+  //   category are defined within such member functions as they are within
+  //   an implicit object member function).
+  DeclContext *DC = getFunctionLevelDeclContext();
+  if (const auto *Method = dyn_cast<CXXMethodDecl>(DC);
+      Method && Method->isExplicitObjectMemberFunction()) {
+    Diag(Loc, diag::err_invalid_this_use) << 1;
+  } else if (isLambdaCallWithExplicitObjectParameter(CurContext)) {
+    Diag(Loc, diag::err_invalid_this_use) << 1;
+  } else {
+    Diag(Loc, diag::err_invalid_this_use) << 0;
   }
-
-  return BuildCXXThisExpr(Loc, ThisTy, /*IsImplicit=*/false);
+  return true;
 }
 
 Expr *Sema::BuildCXXThisExpr(SourceLocation Loc, QualType Type,
@@ -8642,21 +8658,8 @@ static ExprResult attemptRecovery(Sema &SemaRef,
 
       // Detect and handle the case where the decl might be an implicit
       // member.
-      bool MightBeImplicitMember;
-      if (!Consumer.isAddressOfOperand())
-        MightBeImplicitMember = true;
-      else if (!NewSS.isEmpty())
-        MightBeImplicitMember = false;
-      else if (R.isOverloadedResult())
-        MightBeImplicitMember = false;
-      else if (R.isUnresolvableResult())
-        MightBeImplicitMember = true;
-      else
-        MightBeImplicitMember = isa<FieldDecl>(ND) ||
-                                isa<IndirectFieldDecl>(ND) ||
-                                isa<MSPropertyDecl>(ND);
-
-      if (MightBeImplicitMember)
+      if (SemaRef.isPotentialImplicitMemberAccess(
+              NewSS, R, Consumer.isAddressOfOperand()))
         return SemaRef.BuildPossibleImplicitMemberExpr(
             NewSS, /*TemplateKWLoc*/ SourceLocation(), R,
             /*TemplateArgs*/ nullptr, /*S*/ nullptr);
diff --git a/clang/lib/Sema/SemaExprMember.cpp b/clang/lib/Sema/SemaExprMember.cpp
index 32998ae60eafe2..eeac753a348979 100644
--- a/clang/lib/Sema/SemaExprMember.cpp
+++ b/clang/lib/Sema/SemaExprMember.cpp
@@ -61,6 +61,10 @@ enum IMAKind {
   /// The reference is a contextually-permitted abstract member reference.
   IMA_Abstract,
 
+  /// Whether the context is static is dependent on the enclosing template (i.e.
+  /// in a dependent class scope explicit specialization).
+  IMA_Dependent,
+
   /// The reference may be to an unresolved using declaration and the
   /// context is not an instance method.
   IMA_Unresolved_StaticOrExplicitContext,
@@ -91,10 +95,18 @@ static IMAKind ClassifyImplicitMemberAccess(Sema &SemaRef,
 
   DeclContext *DC = SemaRef.getFunctionLevelDeclContext();
 
-  bool isStaticOrExplicitContext =
-      SemaRef.CXXThisTypeOverride.isNull() &&
-      (!isa<CXXMethodDecl>(DC) || cast<CXXMethodDecl>(DC)->isStatic() ||
-       cast<CXXMethodDecl>(DC)->isExplicitObjectMemberFunction());
+  bool couldInstantiateToStatic = false;
+  bool isStaticOrExplicitContext = SemaRef.CXXThisTypeOverride.isNull();
+
+  if (auto *MD = dyn_cast<CXXMethodDecl>(DC)) {
+    if (MD->isImplicitObjectMemberFunction()) {
+      isStaticOrExplicitContext = false;
+      // A dependent class scope function template explicit specialization
+      // that is neither declared 'static' nor with an explicit object
+      // parameter could instantiate to a static or non-static member function.
+      couldInstantiateToStatic = MD->getDependentSpecializationInfo();
+    }
+  }
 
   if (R.isUnresolvableResult())
     return isStaticOrExplicitContext ? IMA_Unresolved_StaticOrExplicitContext
@@ -123,6 +135,9 @@ static IMAKind ClassifyImplicitMemberAccess(Sema &SemaRef,
   if (Classes.empty())
     return IMA_Static;
 
+  if (couldInstantiateToStatic)
+    return IMA_Dependent;
+
   // C++11 [expr.prim.general]p12:
   //   An id-expression that denotes a non-static data member or non-static
   //   member function of a class can only be used:
@@ -263,32 +278,52 @@ static void diagnoseInstanceReference(Sema &SemaRef,
   }
 }
 
+bool Sema::isPotentialImplicitMemberAccess(const CXXScopeSpec &SS,
+                                           LookupResult &R,
+                                           bool IsAddressOfOperand) {
+  if (!getLangOpts().CPlusPlus)
+    return false;
+  else if (R.empty() || !R.begin()->isCXXClassMember())
+    return false;
+  else if (!IsAddressOfOperand)
+    return true;
+  else if (!SS.isEmpty())
+    return false;
+  else if (R.isOverloadedResult())
+    return false;
+  else if (R.isUnresolvableResult())
+    return true;
+  else
+    return isa<FieldDecl, IndirectFieldDecl, MSPropertyDecl>(R.getFoundDecl());
+}
+
 /// Builds an expression which might be an implicit member expression.
 ExprResult Sema::BuildPossibleImplicitMemberExpr(
     const CXXScopeSpec &SS, SourceLocation TemplateKWLoc, LookupResult &R,
-    const TemplateArgumentListInfo *TemplateArgs, const Scope *S,
-    UnresolvedLookupExpr *AsULE) {
-  switch (ClassifyImplicitMemberAccess(*this, R)) {
+    const TemplateArgumentListInfo *TemplateArgs, const Scope *S) {
+  switch (IMAKind Classification = ClassifyImplicitMemberAccess(*this, R)) {
   case IMA_Instance:
-    return BuildImplicitMemberExpr(SS, TemplateKWLoc, R, TemplateArgs, true, S);
-
   case IMA_Mixed:
   case IMA_Mixed_Unrelated:
   case IMA_Unresolved:
-    return BuildImplicitMemberExpr(SS, TemplateKWLoc, R, TemplateArgs, false,
-                                   S);
-
+    return BuildImplicitMemberExpr(
+        SS, TemplateKWLoc, R, TemplateArgs,
+        /*IsKnownInstance=*/Classification == IMA_Instance, S);
   case IMA_Field_Uneval_Context:
     Diag(R.getNameLoc(), diag::warn_cxx98_compat_non_static_member_use)
       << R.getLookupNameInfo().getName();
     [[fallthrough]];
   case IMA_Static:
   case IMA_Abstract:
+  case IMA_Dependent:
   case IMA_Mixed_StaticOrExplicitContext:
   case IMA_Unresolved_StaticOrExplicitContext:
     if (TemplateArgs || TemplateKWLoc.isValid())
-      return BuildTemplateIdExpr(SS, TemplateKWLoc, R, false, TemplateArgs);
-    return AsULE ? AsULE : BuildDeclarationNameExpr(SS, R, false);
+      return BuildTemplateIdExpr(SS, TemplateKWLoc, R, /*RequiresADL=*/false,
+                                 TemplateArgs);
+    return BuildDeclarationNameExpr(
+        SS, R, /*NeedsADL=*/false, /*AcceptInvalidDecl=*/false,
+        /*NeedUnresolved=*/Classification == IMA_Dependent);
 
   case IMA_Error_StaticOrExplicitContext:
   case IMA_Error_Unrelated:
diff --git a/clang/lib/Sema/SemaOpenMP.cpp b/clang/lib/Sema/SemaOpenMP.cpp
index e9efb4721133fe..ca0ad827760bea 100644
--- a/clang/lib/Sema/SemaOpenMP.cpp
+++ b/clang/lib/Sema/SemaOpenMP.cpp
@@ -19280,7 +19280,8 @@ buildDeclareReductionRef(Sema &SemaRef, SourceLocation Loc, SourceRange Range,
     return UnresolvedLookupExpr::Create(
         SemaRef.Context, /*NamingClass=*/nullptr,
         ReductionIdScopeSpec.getWithLocInContext(SemaRef.Context), ReductionId,
-        /*ADL=*/true, /*Overloaded=*/true, ResSet.begin(), ResSet.end());
+        /*ADL=*/true, /*Overloaded=*/true, ResSet.begin(), ResSet.end(),
+        /*KnownDependent=*/false);
   }
   // Lookup inside the classes.
   // C++ [over.match.oper]p3:
@@ -22129,7 +22130,8 @@ static ExprResult buildUserDefinedMapperRef(Sema &SemaRef, Scope *S,
     return UnresolvedLookupExpr::Create(
         SemaRef.Context, /*NamingClass=*/nullptr,
         MapperIdScopeSpec.getWithLocInContext(SemaRef.Context), MapperId,
-        /*ADL=*/false, /*Overloaded=*/true, URS.begin(), URS.end());
+        /*ADL=*/false, /*Overloaded=*/true, URS.begin(), URS.end(),
+        /*KnownDependent=*/false);
   }
   SourceLocation Loc = MapperId.getLoc();
   // [OpenMP 5.0], 2.19.7.3 declare mapper Directive, Restrictions
diff --git a/clang/lib/Sema/SemaOverload.cpp b/clang/lib/Sema/SemaOverload.cpp
index 675eb6ec05e78e..c159c35a17d1a7 100644
--- a/clang/lib/Sema/SemaOverload.cpp
+++ b/clang/lib/Sema/SemaOverload.cpp
@@ -14271,7 +14271,8 @@ ExprResult Sema::CreateUnresolvedLookupExpr(CXXRecordDecl *NamingClass,
                                             bool PerformADL) {
   return UnresolvedLookupExpr::Create(Context, NamingClass, NNSLoc, DNI,
                                       PerformADL, IsOverloaded(Fns),
-                                      Fns.begin(), Fns.end());
+                                      Fns.begin(), Fns.end(),
+                                      /*KnownDependent=*/false);
 }
 
 ExprResult Sema::BuildCXXMemberCallExpr(Expr *E, NamedDecl *FoundDecl,
diff --git a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
index 02d0b35ce940f1..21a139e434cb73 100644
--- a/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/clang/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -5097,6 +5097,14 @@ void Sema::InstantiateFunctionDefinition(SourceLocation PointOfInstantiation,
   EnterExpressionEvaluationContext EvalContext(
       *this, Sema::ExpressionEvaluationContext::PotentiallyEvaluated);
 
+  Qualifiers ThisTypeQuals;
+  CXXRecordDecl *ThisContext = nullptr;
+  if (CXXMethodDecl *Method = dyn_cast<CXXMethodDecl>(Function)) {
+    ThisContext = Method->getParent();
+    ThisTypeQuals = Method->getMethodQualifiers();
+  }
+  CXXThisScopeRAII ThisScope(*this, ThisContext, ThisTypeQuals);
+
   // Introduce a new scope where local variable instantiations will be
   // recorded, unless we're actually a member function within a local
   // class, in which case we need to merge our results with the parent
diff --git a/clang/lib/Sema/TreeTransform.h b/clang/lib/Sema/TreeTransform.h
index fdf84c512c4931..c7928ee0856866 100644
--- a/clang/lib/Sema/TreeTransform.h
+++ b/clang/lib/Sema/TreeTransform.h
@@ -795,6 +795,9 @@ class TreeTransform {
       ParenExpr *PE, DependentScopeDeclRefExpr *DRE, bool IsAddressOfOperand,
       TypeSourceInfo **RecoveryTSI);
 
+  ExprResult TransformUnresolvedLookupExpr(UnresolvedLookupExpr *E,
+                                           bool IsAddressOfOperand);
+
   StmtResult TransformOMPExecutableDirective(OMPExecutableDirective *S);
 
 // FIXME: We use LLVM_ATTRIBUTE_NOINLINE because inlining causes a ridiculous
@@ -3309,12 +3312,13 @@ class TreeTransform {
 
   /// Build a new C++ "this" expression.
   ///
-  /// By default, builds a new "this" expression without performing any
-  /// semantic analysis. Subclasses may override this routine to provide
-  /// different behavior.
+  /// By default, performs semantic analysis to build a new "this" expression.
+  /// Subclasses may override this routine to provide different behavior.
   ExprResult RebuildCXXThisExpr(SourceLocation ThisLoc,
                                 QualType ThisType,
                                 bool isImplicit) {
+    if (getSema().CheckCXXThisType(ThisLoc, ThisType))
+      return ExprError();
     return getSema().BuildCXXThisExpr(ThisLoc, ThisType, isImplicit);
   }
 
@@ -10426,7 +10430,7 @@ TreeTransform<Derived>::TransformOMPReductionClause(OMPReductionClause *C) {
           SemaRef.Context, /*NamingClass=*/nullptr,
           ReductionIdScopeSpec.getWithLocInContext(SemaRef.Context),
           NameInfo, /*ADL=*/true, ULE->isOverloaded(),
-          Decls.begin(), Decls.end()));
+          Decls.begin(), Decls.end(), /*KnownDependent=*/false));
     } else
       UnresolvedReductions.push_back(nullptr);
   }
@@ -10472,7 +10476,8 @@ OMPClause *TreeTransform<Derived>::TransformOMPTaskReductionClause(
       UnresolvedReductions.push_back(UnresolvedLookupExpr::Create(
           SemaRef.Context, /*NamingClass=*/nullptr,
           ReductionIdScopeSpec.getWithLocInContext(SemaRef.Context), NameInfo,
-          /*ADL=*/true, ULE->isOverloaded(), Decls.begin(), Decls.end()));
+          /*ADL=*/true, ULE->isOverloaded(), Decls.begin(), Decls.end(),
+          /*KnownDependent=*/false));
     } else
       UnresolvedReductions.push_back(nullptr);
   }
@@ -10517,7 +10522,8 @@ TreeTransform<Derived>::TransformOMPInReductionClause(OMPInReductionClause *C) {
       UnresolvedReductions.push_back(UnresolvedLookupExpr::Create(
           SemaRef.Context, /*NamingClass=*/nullptr,
           ReductionIdScopeSpec.getWithLocInContext(SemaRef.Context), NameInfo,
-          /*ADL=*/true, ULE->isOverloaded(), Decls.begin(), Decls.end()));
+          /*ADL=*/true, ULE->isOverloaded(), Decls.begin(), Decls.end(),
+          /*KnownDependent=*/false));
     } else
       UnresolvedReductions.push_back(nullptr);
   }
@@ -10699,7 +10705,7 @@ bool transformOMPMappableExprListClause(
           TT.getSema().Context, /*NamingClass=*/nullptr,
           MapperIdScopeSpec.getWithLocInContext(TT.getSema().Context),
           MapperIdInfo, /*ADL=*/true, ULE->isOverloaded(), Decls.begin(),
-          Decls.end()));
+          Decls.end(), /*KnownDependent=*/false));
     } else {
       UnresolvedMappers.push_back(nullptr);
     }
@@ -11365,7 +11371,11 @@ template<typename Derived>
 ExprResult
 TreeTransform<Derived>::TransformAddressOfOperand(Expr *E) {
   if (DependentScopeDeclRefExpr *DRE = dyn_cast<DependentScopeDeclRefExpr>(E))
-    return getDerived().TransformDependentScopeDeclRefExpr(DRE, true, nullptr);
+    return getDerived().TransformDependentScopeDeclRefExpr(
+        DRE, /*IsAddressOfOperand=*/true, nullptr);
+  else if (UnresolvedLookupExpr *ULE = dyn_cast<UnresolvedLookupExpr>(E))
+    return getDerived().TransformUnresolvedLookupExpr(
+        ULE, /*IsAddressOfOperand=*/true);
   else
     return getDerived().TransformExpr(E);
 }
@@ -13071,10 +13081,16 @@ bool TreeTransform<Derived>::TransformOverloadExprDecls(OverloadExpr *Old,
   return false;
 }
 
-template<typename Derived>
+template <typename Derived>
+ExprResult TreeTransform<Derived>::TransformUnresolvedLookupExpr(
+    UnresolvedLookupExpr *Old) {
+  return TransformUnresolvedLookupExpr(Old, /*IsAddressOfOperand=*/false);
+}
+
+template <typename Derived>
 ExprResult
-TreeTransform<Derived>::TransformUnresolvedLookupExpr(
-                                                  UnresolvedLookupExpr *Old) {
+TreeTransform<Derived>::TransformUnresolvedLookupExpr(UnresolvedLookupExpr *Old,
+                                                      bool IsAddressOfOperand) {
   LookupResult R(SemaRef, Old->getName(), Old->getNameLoc(),
                  Sema::LookupOrdinaryName);
 
@@ -13106,26 +13122,8 @@ TreeTransform<Derived>::TransformUnresolvedLookupExpr(
     R.setNamingClass(NamingClass);
   }
 
+  // Rebuild the template arguments, if any.
   SourceLocation TemplateKWLoc = Old->getTemplateKeywordLoc();
-
-  // If we have neither explicit template arguments, nor the template keyword,
-  // it's a normal declaration name or member reference.
-  if (!Old->hasExplicitTemplateArgs() && !TemplateKWLoc.isValid()) {
-    NamedDecl *D = R.getAsSingle<NamedDecl>();
-    // In a C++11 unevaluated context, an UnresolvedLookupExpr might refer to an
-    // instance member. In other contexts, BuildPossibleImplicitMemberExpr will
-    // give a good diagnostic.
-    if (D && D->isCXXInstanceMember()) {
-      return SemaRef.BuildPossibleImplicitMemberExpr(SS, TemplateKWLoc, R,
-                                                     /*TemplateArgs=*/nullptr,
-                                                     /*Scope=*/nullptr);
-    }
-
-    return getDerived().RebuildDeclarationNameExpr(SS, R, Old->requiresADL());
-  }
-
-  // If we have template arguments, rebuild them, then rebuild the
-  // templateid expression.
   TemplateArgumentListInfo TransArgs(Old->getLAngleLoc(), Old->getRAngleLoc());
   if (Old->hasExplicitTemplateArgs() &&
       getDerived().TransformTemplateArguments(Old->getTemplateArgs(),
@@ -13135,6 +13133,23 @@ TreeTransform<Derived>::TransformUnresolvedLookupExpr(
     return ExprError();
   }
 
+  // An UnresolvedLookupExpr can refer to a class member. This occurs e.g. when
+  // a non-static data member is named in an unevaluated operand, or when
+  // a member is named in a dependent class scope function template explicit
+  // specialization that is neither declared static nor with an explicit object
+  // parameter.
+  if (SemaRef.isPotentialImplicitMemberAccess(SS, R, IsAddressOfOperand))
+    return SemaRef.BuildPossibleImplicitMemberExpr(
+        SS, TemplateKWLoc, R,
+        Old->hasExplicitTemplateArgs() ? &TransArgs : nullptr,
+        /*S=*/nullptr);
+
+  // If we have neither explicit template arguments, nor the template keyword,
+  // it's a normal declaration name or member reference.
+  if (!Old->hasExplicitTemplateArgs() && !TemplateKWLoc.isValid())
+    return getDerived().RebuildDeclarationNameExpr(SS, R, Old->requiresADL());
+
+  // If we have template arguments, then rebuild the template-id expression.
   return getDerived().RebuildTemplateIdExpr(SS, TemplateKWLoc, R,
                                             Old->requiresADL(), &TransArgs);
 }
diff --git a/clang/test/SemaTemplate/instantiate-using-decl.cpp b/clang/test/SemaTemplate/instantiate-using-decl.cpp
index 0bbb3ca9c88c8b..28d83764385131 100644
--- a/clang/test/SemaTemplate/instantiate-using-decl.cpp
+++ b/clang/test/SemaTemplate/instantiate-using-decl.cpp
@@ -121,7 +121,7 @@ template <typename Scalar> struct Derived : Base<Scalar> {
     (void)&field;
     // expected-error at +1 {{call to non-static member function without an object argument}}
     (void)method;
-    // expected-error at +1 {{call to non-static member function without an object argument}}
+    // expected-error at +1 {{must explicitly qualify name of member function when taking its address}}
     (void)&method;
     // expected-error at +1 {{call to non-static member function without an object argument}}
     method();
diff --git a/clang/test/SemaTemplate/ms-function-specialization-class-scope.cpp b/clang/test/SemaTemplate/ms-function-specialization-class-scope.cpp
index dcab9bfaeabcb0..76e84e2bcbda7f 100644
--- a/clang/test/SemaTemplate/ms-function-specialization-class-scope.cpp
+++ b/clang/test/SemaTemplate/ms-function-specialization-class-scope.cpp
@@ -1,7 +1,6 @@
-// RUN: %clang_cc1 -fms-extensions -fsyntax-only -verify %s
-// RUN: %clang_cc1 -fms-extensions -fdelayed-template-parsing -fsyntax-only -verify %s
+// RUN: %clang_cc1 -fms-extensions -fsyntax-only -Wno-unused-value -verify %s
+// RUN: %clang_cc1 -fms-extensions -fdelayed-template-parsing -fsyntax-only -Wno-unused-value -verify %s
 
-// expected-no-diagnostics
 class A {
 public:
   template<class U> A(U p) {}
@@ -76,3 +75,199 @@ struct S {
   int f<0>(int);
 };
 }
+
+namespace UsesThis {
+  template<typename T>
+  struct A {
+    int x;
+
+    static inline int y;
+
+    template<typename U = void>
+    static void f();
+
+    template<typename U = void>
+    void g();
+
+    template<typename U>
+    static auto h() -> A*;
+
+    void i();
+
+    static void j();
+
+    template<>
+    void f<int>() {
+      this->x; // expected-error {{invalid use of 'this' outside of a non-static member function}}
+      x; // expected-error {{invalid use of member 'x' in static member function}}
+      A::x; // expected-error {{invalid use of member 'x' in static member function}}
+      +x; // expected-error {{invalid use of member 'x' in static member function}}
+      +A::x; // expected-error {{invalid use of member 'x' in static member function}}
+      &x; // expected-error {{invalid use of member 'x' in static member function}}
+      &A::x;
+      this->y; // expected-error {{invalid use of 'this' outside of a non-static member function}}
+      y;
+      A::y;
+      +y;
+      +A::y;
+      &y;
+      &A::y;
+      f();
+      f<void>();
+      g(); // expected-error {{call to non-static member function without an object argument}}
+      g<void>(); // expected-error {{call to non-static member function without an object argument}}
+      i(); // expected-error {{call to non-static member function without an object argument}}
+      j();
+      &i; // expected-error 2{{must explicitly qualify name of member function when taking its address}}
+      &j;
+      &A::i;
+      &A::j;
+    }
+
+    template<>
+    void g<int>() {
+      this->x;
+      x;
+      A::x;
+      +x;
+      +A::x;
+      &x;
+      &A::x;
+      this->y;
+      y;
+      A::y;
+      +y;
+      +A::y;
+      &y;
+      &A::y;
+      f();
+      f<void>();
+      g();
+      g<void>();
+      i();
+      j();
+      &i; // expected-error 2{{must explicitly qualify name of member function when taking its address}}
+      &j;
+      &A::i;
+      &A::j;
+    }
+
+    template<>
+    auto h<int>() -> decltype(this); // expected-error {{'this' cannot be used in a static member function declaration}}
+  };
+
+  template struct A<int>; // expected-note 3{{in instantiation of}}
+
+  template <typename T>
+  struct Foo {
+    template <typename X>
+    int bar(X x) {
+      return 0;
+    }
+
+    template <>
+    int bar(int x) {
+      return bar(5.0); // ok
+    }
+  };
+
+  void call() {
+    Foo<double> f;
+    f.bar(1);
+  }
+
+  struct B {
+    int x0;
+    static inline int y0;
+
+    int f0(int);
+    static int g0(int);
+  };
+
+  template<typename T>
+  struct D : B {
+    int x1;
+    static inline int y1;
+
+    int f1(int);
+    static int g1(int);
+
+    template<typename U>
+    void non_static_spec(U);
+
+    template<typename U>
+    static void static_spec(U);
+
+    template<>
+    void non_static_spec(int z) {
+      ++z;
+      ++x0;
+      ++x1;
+      ++y0;
+      ++y1;
+
+      f0(0);
+      f0(z);
+      f0(x0);
+      f0(x1);
+      f0(y0);
+      f0(y1);
+      g0(0);
+      g0(z);
+      g0(x0);
+      g0(x1);
+      g0(y0);
+      g0(y1);
+
+      f1(0);
+      f1(z);
+      f1(x0);
+      f1(x1);
+      f1(y0);
+      f1(y1);
+      g1(0);
+      g1(z);
+      g1(x0);
+      g1(x1);
+      g1(y0);
+      g1(y1);
+    }
+
+    template<>
+    void static_spec(int z) {
+      ++z;
+      ++x0; // expected-error {{invalid use of member 'x0' in static member function}}
+      ++x1; // expected-error {{invalid use of member 'x1' in static member function}}
+      ++y0;
+      ++y1;
+
+      f0(0); // expected-error {{call to non-static member function without an object argument}}
+      f0(z); // expected-error {{call to non-static member function without an object argument}}
+      f0(x0); // expected-error {{call to non-static member function without an object argument}}
+      f0(x1); // expected-error {{call to non-static member function without an object argument}}
+      f0(y0); // expected-error {{call to non-static member function without an object argument}}
+      f0(y1); // expected-error {{call to non-static member function without an object argument}}
+      g0(0);
+      g0(z);
+      g0(x0); // expected-error {{invalid use of member 'x0' in static member function}}
+      g0(x1); // expected-error {{invalid use of member 'x1' in static member function}}
+      g0(y0);
+      g0(y1);
+
+      f1(0); // expected-error {{call to non-static member function without an object argument}}
+      f1(z); // expected-error {{call to non-static member function without an object argument}}
+      f1(x0); // expected-error {{call to non-static member function without an object argument}}
+      f1(x1); // expected-error {{call to non-static member function without an object argument}}
+      f1(y0); // expected-error {{call to non-static member function without an object argument}}
+      f1(y1); // expected-error {{call to non-static member function without an object argument}}
+      g1(0);
+      g1(z);
+      g1(x0); // expected-error {{invalid use of member 'x0' in static member function}}
+      g1(x1); // expected-error {{invalid use of member 'x1' in static member function}}
+      g1(y0);
+      g1(y1);
+    }
+  };
+
+  template struct D<int>; // expected-note {{in instantiation of}}
+}



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