Revert "Reapply "[Clang][Sema] Refactor collection of multi-level template argument lists (#106585)" (#111173)"

clang/docs/ReleaseNotes.rst

@@ -477,9 +477,6 @@ Bug Fixes to C++ Support
   in certain friend declarations. (#GH93099)
 - Clang now instantiates the correct lambda call operator when a lambda's class type is
   merged across modules. (#GH110401)
-- Clang now uses the correct set of template argument lists when comparing the constraints of
-  out-of-line definitions and member templates explicitly specialized for a given implicit instantiation of
-  a class template. (#GH102320)
 - Fix a crash when parsing a pseudo destructor involving an invalid type. (#GH111460)
 
 Bug Fixes to AST Handling

clang/include/clang/AST/DeclTemplate.h

@@ -781,11 +781,15 @@ class RedeclarableTemplateDecl : public TemplateDecl,
                              EntryType *Entry, void *InsertPos);
 
   struct CommonBase {
-    CommonBase() {}
+    CommonBase() : InstantiatedFromMember(nullptr, false) {}
 
     /// The template from which this was most
     /// directly instantiated (or null).
-    RedeclarableTemplateDecl *InstantiatedFromMember = nullptr;
+    ///
+    /// The boolean value indicates whether this template
+    /// was explicitly specialized.
+    llvm::PointerIntPair<RedeclarableTemplateDecl*, 1, bool>
+      InstantiatedFromMember;
 
     /// If non-null, points to an array of specializations (including
     /// partial specializations) known only by their external declaration IDs.
@@ -805,19 +809,14 @@ class RedeclarableTemplateDecl : public TemplateDecl,
   };
 
   /// Pointer to the common data shared by all declarations of this
-  /// template, and a flag indicating if the template is a member
-  /// specialization.
-  mutable llvm::PointerIntPair<CommonBase *, 1, bool> Common;
-
-  CommonBase *getCommonPtrInternal() const { return Common.getPointer(); }
+  /// template.
+  mutable CommonBase *Common = nullptr;
 
   /// Retrieves the "common" pointer shared by all (re-)declarations of
   /// the same template. Calling this routine may implicitly allocate memory
   /// for the common pointer.
   CommonBase *getCommonPtr() const;
 
-  void setCommonPtr(CommonBase *C) const { Common.setPointer(C); }
-
   virtual CommonBase *newCommon(ASTContext &C) const = 0;
 
   // Construct a template decl with name, parameters, and templated element.
@@ -858,12 +857,15 @@ class RedeclarableTemplateDecl : public TemplateDecl,
   /// template<> template<typename T>
   /// struct X<int>::Inner { /* ... */ };
   /// \endcode
-  bool isMemberSpecialization() const { return Common.getInt(); }
+  bool isMemberSpecialization() const {
+    return getCommonPtr()->InstantiatedFromMember.getInt();
+  }
 
   /// Note that this member template is a specialization.
   void setMemberSpecialization() {
-    assert(!isMemberSpecialization() && "already a member specialization");
-    Common.setInt(true);
+    assert(getCommonPtr()->InstantiatedFromMember.getPointer() &&
+           "Only member templates can be member template specializations");
+    getCommonPtr()->InstantiatedFromMember.setInt(true);
   }
 
   /// Retrieve the member template from which this template was
@@ -903,12 +905,12 @@ class RedeclarableTemplateDecl : public TemplateDecl,
   /// void X<T>::f(T, U);
   /// \endcode
   RedeclarableTemplateDecl *getInstantiatedFromMemberTemplate() const {
-    return getCommonPtr()->InstantiatedFromMember;
+    return getCommonPtr()->InstantiatedFromMember.getPointer();
   }
 
   void setInstantiatedFromMemberTemplate(RedeclarableTemplateDecl *TD) {
-    assert(!getCommonPtr()->InstantiatedFromMember);
-    getCommonPtr()->InstantiatedFromMember = TD;
+    assert(!getCommonPtr()->InstantiatedFromMember.getPointer());
+    getCommonPtr()->InstantiatedFromMember.setPointer(TD);
   }
 
   /// Retrieve the "injected" template arguments that correspond to the
@@ -1987,8 +1989,6 @@ class ClassTemplateSpecializationDecl : public CXXRecordDecl,
   /// template arguments have been deduced.
   void setInstantiationOf(ClassTemplatePartialSpecializationDecl *PartialSpec,
                           const TemplateArgumentList *TemplateArgs) {
-    assert(!isa<ClassTemplatePartialSpecializationDecl>(this) &&
-           "A partial specialization cannot be instantiated from a template");
     assert(!SpecializedTemplate.is<SpecializedPartialSpecialization*>() &&
            "Already set to a class template partial specialization!");
     auto *PS = new (getASTContext()) SpecializedPartialSpecialization();
@@ -2000,8 +2000,6 @@ class ClassTemplateSpecializationDecl : public CXXRecordDecl,
   /// Note that this class template specialization is an instantiation
   /// of the given class template.
   void setInstantiationOf(ClassTemplateDecl *TemplDecl) {
-    assert(!isa<ClassTemplatePartialSpecializationDecl>(this) &&
-           "A partial specialization cannot be instantiated from a template");
     assert(!SpecializedTemplate.is<SpecializedPartialSpecialization*>() &&
            "Previously set to a class template partial specialization!");
     SpecializedTemplate = TemplDecl;
@@ -2189,11 +2187,18 @@ class ClassTemplatePartialSpecializationDecl
   /// struct X<int>::Inner<T*> { /* ... */ };
   /// \endcode
   bool isMemberSpecialization() const {
-    return InstantiatedFromMember.getInt();
+    const auto *First =
+        cast<ClassTemplatePartialSpecializationDecl>(getFirstDecl());
+    return First->InstantiatedFromMember.getInt();
   }
 
   /// Note that this member template is a specialization.
-  void setMemberSpecialization() { return InstantiatedFromMember.setInt(true); }
+  void setMemberSpecialization() {
+    auto *First = cast<ClassTemplatePartialSpecializationDecl>(getFirstDecl());
+    assert(First->InstantiatedFromMember.getPointer() &&
+           "Only member templates can be member template specializations");
+    return First->InstantiatedFromMember.setInt(true);
+  }
 
   /// Retrieves the injected specialization type for this partial
   /// specialization.  This is not the same as the type-decl-type for
@@ -2263,6 +2268,10 @@ class ClassTemplateDecl : public RedeclarableTemplateDecl {
     return static_cast<Common *>(RedeclarableTemplateDecl::getCommonPtr());
   }
 
+  void setCommonPtr(Common *C) {
+    RedeclarableTemplateDecl::Common = C;
+  }
+
 public:
 
   friend class ASTDeclReader;
@@ -2745,8 +2754,6 @@ class VarTemplateSpecializationDecl : public VarDecl,
   /// template arguments have been deduced.
   void setInstantiationOf(VarTemplatePartialSpecializationDecl *PartialSpec,
                           const TemplateArgumentList *TemplateArgs) {
-    assert(!isa<VarTemplatePartialSpecializationDecl>(this) &&
-           "A partial specialization cannot be instantiated from a template");
     assert(!SpecializedTemplate.is<SpecializedPartialSpecialization *>() &&
            "Already set to a variable template partial specialization!");
     auto *PS = new (getASTContext()) SpecializedPartialSpecialization();
@@ -2758,8 +2765,6 @@ class VarTemplateSpecializationDecl : public VarDecl,
   /// Note that this variable template specialization is an instantiation
   /// of the given variable template.
   void setInstantiationOf(VarTemplateDecl *TemplDecl) {
-    assert(!isa<VarTemplatePartialSpecializationDecl>(this) &&
-           "A partial specialization cannot be instantiated from a template");
     assert(!SpecializedTemplate.is<SpecializedPartialSpecialization *>() &&
            "Previously set to a variable template partial specialization!");
     SpecializedTemplate = TemplDecl;
@@ -2944,11 +2949,18 @@ class VarTemplatePartialSpecializationDecl
   /// U* X<int>::Inner<T*> = (T*)(0) + 1;
   /// \endcode
   bool isMemberSpecialization() const {
-    return InstantiatedFromMember.getInt();
+    const auto *First =
+        cast<VarTemplatePartialSpecializationDecl>(getFirstDecl());
+    return First->InstantiatedFromMember.getInt();
   }
 
   /// Note that this member template is a specialization.
-  void setMemberSpecialization() { return InstantiatedFromMember.setInt(true); }
+  void setMemberSpecialization() {
+    auto *First = cast<VarTemplatePartialSpecializationDecl>(getFirstDecl());
+    assert(First->InstantiatedFromMember.getPointer() &&
+           "Only member templates can be member template specializations");
+    return First->InstantiatedFromMember.setInt(true);
+  }
 
   SourceRange getSourceRange() const override LLVM_READONLY;
 

clang/include/clang/Sema/Sema.h

@@ -11325,9 +11325,9 @@ class Sema final : public SemaBase {
       CXXScopeSpec &SS, IdentifierInfo *Name, SourceLocation NameLoc,
       const ParsedAttributesView &Attr, TemplateParameterList *TemplateParams,
       AccessSpecifier AS, SourceLocation ModulePrivateLoc,
-      SourceLocation FriendLoc,
-      ArrayRef<TemplateParameterList *> OuterTemplateParamLists,
-      bool IsMemberSpecialization, SkipBodyInfo *SkipBody = nullptr);
+      SourceLocation FriendLoc, unsigned NumOuterTemplateParamLists,
+      TemplateParameterList **OuterTemplateParamLists,
+      SkipBodyInfo *SkipBody = nullptr);
 
   /// Translates template arguments as provided by the parser
   /// into template arguments used by semantic analysis.
@@ -11366,8 +11366,7 @@ class Sema final : public SemaBase {
   DeclResult ActOnVarTemplateSpecialization(
       Scope *S, Declarator &D, TypeSourceInfo *DI, LookupResult &Previous,
       SourceLocation TemplateKWLoc, TemplateParameterList *TemplateParams,
-      StorageClass SC, bool IsPartialSpecialization,
-      bool IsMemberSpecialization);
+      StorageClass SC, bool IsPartialSpecialization);
 
   /// Get the specialization of the given variable template corresponding to
   /// the specified argument list, or a null-but-valid result if the arguments
@@ -13008,14 +13007,28 @@ class Sema final : public SemaBase {
   /// dealing with a specialization. This is only relevant for function
   /// template specializations.
   ///
+  /// \param Pattern If non-NULL, indicates the pattern from which we will be
+  /// instantiating the definition of the given declaration, \p ND. This is
+  /// used to determine the proper set of template instantiation arguments for
+  /// friend function template specializations.
+  ///
   /// \param ForConstraintInstantiation when collecting arguments,
   /// ForConstraintInstantiation indicates we should continue looking when
   /// encountering a lambda generic call operator, and continue looking for
   /// arguments on an enclosing class template.
+  ///
+  /// \param SkipForSpecialization when specified, any template specializations
+  /// in a traversal would be ignored.
+  /// \param ForDefaultArgumentSubstitution indicates we should continue looking
+  /// when encountering a specialized member function template, rather than
+  /// returning immediately.
   MultiLevelTemplateArgumentList getTemplateInstantiationArgs(
       const NamedDecl *D, const DeclContext *DC = nullptr, bool Final = false,
       std::optional<ArrayRef<TemplateArgument>> Innermost = std::nullopt,
-      bool RelativeToPrimary = false, bool ForConstraintInstantiation = false);
+      bool RelativeToPrimary = false, const FunctionDecl *Pattern = nullptr,
+      bool ForConstraintInstantiation = false,
+      bool SkipForSpecialization = false,
+      bool ForDefaultArgumentSubstitution = false);
 
   /// RAII object to handle the state changes required to synthesize
   /// a function body.

clang/lib/AST/Decl.cpp

@@ -2696,27 +2696,21 @@ VarDecl *VarDecl::getTemplateInstantiationPattern() const {
     if (isTemplateInstantiation(VDTemplSpec->getTemplateSpecializationKind())) {
       auto From = VDTemplSpec->getInstantiatedFrom();
       if (auto *VTD = From.dyn_cast<VarTemplateDecl *>()) {
-        while (true) {
-          VTD = VTD->getMostRecentDecl();
-          if (VTD->isMemberSpecialization())
-            break;
-          if (auto *NewVTD = VTD->getInstantiatedFromMemberTemplate())
-            VTD = NewVTD;
-          else
+        while (!VTD->isMemberSpecialization()) {
+          auto *NewVTD = VTD->getInstantiatedFromMemberTemplate();
+          if (!NewVTD)
             break;
+          VTD = NewVTD;
         }
         return getDefinitionOrSelf(VTD->getTemplatedDecl());
       }
       if (auto *VTPSD =
               From.dyn_cast<VarTemplatePartialSpecializationDecl *>()) {
-        while (true) {
-          VTPSD = VTPSD->getMostRecentDecl();
-          if (VTPSD->isMemberSpecialization())
-            break;
-          if (auto *NewVTPSD = VTPSD->getInstantiatedFromMember())
-            VTPSD = NewVTPSD;
-          else
+        while (!VTPSD->isMemberSpecialization()) {
+          auto *NewVTPSD = VTPSD->getInstantiatedFromMember();
+          if (!NewVTPSD)
             break;
+          VTPSD = NewVTPSD;
         }
         return getDefinitionOrSelf<VarDecl>(VTPSD);
       }
@@ -2725,17 +2719,15 @@ VarDecl *VarDecl::getTemplateInstantiationPattern() const {
 
   // If this is the pattern of a variable template, find where it was
   // instantiated from. FIXME: Is this necessary?
-  if (VarTemplateDecl *VTD = VD->getDescribedVarTemplate()) {
-    while (true) {
-      VTD = VTD->getMostRecentDecl();
-      if (VTD->isMemberSpecialization())
-        break;
-      if (auto *NewVTD = VTD->getInstantiatedFromMemberTemplate())
-        VTD = NewVTD;
-      else
+  if (VarTemplateDecl *VarTemplate = VD->getDescribedVarTemplate()) {
+    while (!VarTemplate->isMemberSpecialization()) {
+      auto *NewVT = VarTemplate->getInstantiatedFromMemberTemplate();
+      if (!NewVT)
         break;
+      VarTemplate = NewVT;
     }
-    return getDefinitionOrSelf(VTD->getTemplatedDecl());
+
+    return getDefinitionOrSelf(VarTemplate->getTemplatedDecl());
   }
 
   if (VD == this)
@@ -4150,14 +4142,11 @@ FunctionDecl::getTemplateInstantiationPattern(bool ForDefinition) const {
   if (FunctionTemplateDecl *Primary = getPrimaryTemplate()) {
     // If we hit a point where the user provided a specialization of this
     // template, we're done looking.
-    while (true) {
-      Primary = Primary->getMostRecentDecl();
-      if (ForDefinition && Primary->isMemberSpecialization())
-        break;
-      if (auto *NewPrimary = Primary->getInstantiatedFromMemberTemplate())
-        Primary = NewPrimary;
-      else
+    while (!ForDefinition || !Primary->isMemberSpecialization()) {
+      auto *NewPrimary = Primary->getInstantiatedFromMemberTemplate();
+      if (!NewPrimary)
         break;
+      Primary = NewPrimary;
     }
 
     return getDefinitionOrSelf(Primary->getTemplatedDecl());

clang/lib/AST/DeclCXX.cpp

@@ -2023,27 +2023,19 @@ const CXXRecordDecl *CXXRecordDecl::getTemplateInstantiationPattern() const {
   if (auto *TD = dyn_cast<ClassTemplateSpecializationDecl>(this)) {
     auto From = TD->getInstantiatedFrom();
     if (auto *CTD = From.dyn_cast<ClassTemplateDecl *>()) {
-      while (true) {
-        CTD = CTD->getMostRecentDecl();
-        if (CTD->isMemberSpecialization())
-          break;
-        if (auto *NewCTD = CTD->getInstantiatedFromMemberTemplate())
-          CTD = NewCTD;
-        else
+      while (auto *NewCTD = CTD->getInstantiatedFromMemberTemplate()) {
+        if (NewCTD->isMemberSpecialization())
           break;
+        CTD = NewCTD;
       }
       return GetDefinitionOrSelf(CTD->getTemplatedDecl());
     }
     if (auto *CTPSD =
             From.dyn_cast<ClassTemplatePartialSpecializationDecl *>()) {
-      while (true) {
-        CTPSD = CTPSD->getMostRecentDecl();
-        if (CTPSD->isMemberSpecialization())
-          break;
-        if (auto *NewCTPSD = CTPSD->getInstantiatedFromMemberTemplate())
-          CTPSD = NewCTPSD;
-        else
+      while (auto *NewCTPSD = CTPSD->getInstantiatedFromMember()) {
+        if (NewCTPSD->isMemberSpecialization())
           break;
+        CTPSD = NewCTPSD;
       }
       return GetDefinitionOrSelf(CTPSD);
     }