Revert "Reapply "[Clang][Sema] Fix crash when 'this' is used in a dep…

…endent class scope function template specialization that instantiates to a static member function (#87541)" (#88311)"

This reverts commit aa80f3e.

See
#88311 (comment).

There is a fix forward proposed but I am reverting this commit to fix
trunk.

clang/docs/ReleaseNotes.rst

@@ -529,8 +529,6 @@ 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>`_)

clang/include/clang/Sema/Sema.h

@@ -5452,8 +5452,7 @@ class Sema final : public SemaBase {
 
   ExprResult BuildDeclarationNameExpr(const CXXScopeSpec &SS, LookupResult &R,
                                       bool NeedsADL,
-                                      bool AcceptInvalidDecl = false,
-                                      bool NeedUnresolved = false);
+                                      bool AcceptInvalidDecl = false);
   ExprResult BuildDeclarationNameExpr(
       const CXXScopeSpec &SS, const DeclarationNameInfo &NameInfo, NamedDecl *D,
       NamedDecl *FoundD = nullptr,
@@ -6596,10 +6595,7 @@ class Sema final : public SemaBase {
                             SourceLocation RParenLoc);
 
   //// ActOnCXXThis -  Parse 'this' pointer.
-  ExprResult ActOnCXXThis(SourceLocation Loc);
-
-  /// Check whether the type of 'this' is valid in the current context.
-  bool CheckCXXThisType(SourceLocation Loc, QualType Type);
+  ExprResult ActOnCXXThis(SourceLocation loc);
 
   /// Build a CXXThisExpr and mark it referenced in the current context.
   Expr *BuildCXXThisExpr(SourceLocation Loc, QualType Type, bool IsImplicit);
@@ -7022,14 +7018,10 @@ 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);
-
+      const TemplateArgumentListInfo *TemplateArgs, const Scope *S,
+      UnresolvedLookupExpr *AsULE = nullptr);
   ExprResult
   BuildImplicitMemberExpr(const CXXScopeSpec &SS, SourceLocation TemplateKWLoc,
                           LookupResult &R,

clang/lib/Sema/SemaExpr.cpp

@@ -2917,9 +2917,26 @@ 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 (isPotentialImplicitMemberAccess(SS, R, IsAddressOfOperand))
-    return BuildPossibleImplicitMemberExpr(SS, TemplateKWLoc, R, TemplateArgs,
-                                           S);
+  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 (TemplateArgs || TemplateKWLoc.isValid()) {
 
@@ -3430,11 +3447,10 @@ static bool ShouldLookupResultBeMultiVersionOverload(const LookupResult &R) {
 
 ExprResult Sema::BuildDeclarationNameExpr(const CXXScopeSpec &SS,
                                           LookupResult &R, bool NeedsADL,
-                                          bool AcceptInvalidDecl,
-                                          bool NeedUnresolved) {
+                                          bool AcceptInvalidDecl) {
   // If this is a single, fully-resolved result and we don't need ADL,
   // just build an ordinary singleton decl ref.
-  if (!NeedUnresolved && !NeedsADL && R.isSingleResult() &&
+  if (!NeedsADL && R.isSingleResult() &&
       !R.getAsSingle<FunctionTemplateDecl>() &&
       !ShouldLookupResultBeMultiVersionOverload(R))
     return BuildDeclarationNameExpr(SS, R.getLookupNameInfo(), R.getFoundDecl(),

clang/lib/Sema/SemaExprCXX.cpp

@@ -1416,42 +1416,26 @@ bool Sema::CheckCXXThisCapture(SourceLocation Loc, const bool Explicit,
 }
 
 ExprResult Sema::ActOnCXXThis(SourceLocation Loc) {
-  // 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.
+  /// 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.
   QualType ThisTy = getCurrentThisType();
 
-  if (CheckCXXThisType(Loc, ThisTy))
-    return ExprError();
+  if (ThisTy.isNull()) {
+    DeclContext *DC = getFunctionLevelDeclContext();
 
-  return BuildCXXThisExpr(Loc, ThisTy, /*IsImplicit=*/false);
-}
+    if (const auto *Method = dyn_cast<CXXMethodDecl>(DC);
+        Method && Method->isExplicitObjectMemberFunction()) {
+      return Diag(Loc, diag::err_invalid_this_use) << 1;
+    }
 
-bool Sema::CheckCXXThisType(SourceLocation Loc, QualType Type) {
-  if (!Type.isNull())
-    return false;
+    if (isLambdaCallWithExplicitObjectParameter(CurContext))
+      return Diag(Loc, diag::err_invalid_this_use) << 1;
 
-  // 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 Diag(Loc, diag::err_invalid_this_use) << 0;
   }
-  return true;
+
+  return BuildCXXThisExpr(Loc, ThisTy, /*IsImplicit=*/false);
 }
 
 Expr *Sema::BuildCXXThisExpr(SourceLocation Loc, QualType Type,
@@ -8658,8 +8642,21 @@ static ExprResult attemptRecovery(Sema &SemaRef,
 
       // Detect and handle the case where the decl might be an implicit
       // member.
-      if (SemaRef.isPotentialImplicitMemberAccess(
-              NewSS, R, Consumer.isAddressOfOperand()))
+      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)
         return SemaRef.BuildPossibleImplicitMemberExpr(
             NewSS, /*TemplateKWLoc*/ SourceLocation(), R,
             /*TemplateArgs*/ nullptr, /*S*/ nullptr);

clang/lib/Sema/SemaExprMember.cpp

@@ -61,10 +61,6 @@ 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,
@@ -95,18 +91,10 @@ static IMAKind ClassifyImplicitMemberAccess(Sema &SemaRef,
 
   DeclContext *DC = SemaRef.getFunctionLevelDeclContext();
 
-  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();
-    }
-  }
+  bool isStaticOrExplicitContext =
+      SemaRef.CXXThisTypeOverride.isNull() &&
+      (!isa<CXXMethodDecl>(DC) || cast<CXXMethodDecl>(DC)->isStatic() ||
+       cast<CXXMethodDecl>(DC)->isExplicitObjectMemberFunction());
 
   if (R.isUnresolvableResult())
     return isStaticOrExplicitContext ? IMA_Unresolved_StaticOrExplicitContext
@@ -135,9 +123,6 @@ 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:
@@ -278,52 +263,32 @@ 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) {
-  switch (IMAKind Classification = ClassifyImplicitMemberAccess(*this, R)) {
+    const TemplateArgumentListInfo *TemplateArgs, const Scope *S,
+    UnresolvedLookupExpr *AsULE) {
+  switch (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,
-        /*IsKnownInstance=*/Classification == IMA_Instance, S);
+    return BuildImplicitMemberExpr(SS, TemplateKWLoc, R, TemplateArgs, false,
+                                   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, /*RequiresADL=*/false,
-                                 TemplateArgs);
-    return BuildDeclarationNameExpr(
-        SS, R, /*NeedsADL=*/false, /*AcceptInvalidDecl=*/false,
-        /*NeedUnresolved=*/Classification == IMA_Dependent);
+      return BuildTemplateIdExpr(SS, TemplateKWLoc, R, false, TemplateArgs);
+    return AsULE ? AsULE : BuildDeclarationNameExpr(SS, R, false);
 
   case IMA_Error_StaticOrExplicitContext:
   case IMA_Error_Unrelated:

clang/lib/Sema/SemaTemplateInstantiateDecl.cpp

@@ -5097,14 +5097,6 @@ 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