Factor code into CXXRecordDecl::getTemplateInstantiationPattern() helper

[rnk]

Summary

This moves some code from SemaType.cpp's hasVisibleDefinition() into
DeclCXX.cpp so that it can be used elsewhere. I found one other instance
of code trying to do the same thing, there are probably more. Search for
getInstantiatedFrom() to try to find more.

No functionality change.

[rsmith]

LGTM

[rnk]

Closed by commit rL219714 (authored by @rnk).

include/clang/AST/DeclCXX.h

public:
   /// \brief Determine whether this particular class is a specialization or
   /// instantiation of a class template or member class of a class template,
   /// and how it was instantiated or specialized.
   TemplateSpecializationKind getTemplateSpecializationKind() const;
 
   /// \brief Set the kind of specialization or template instantiation this is.
   void setTemplateSpecializationKind(TemplateSpecializationKind TSK);
 
+  /// \brief Retrieve the record declaration from which this record could be
+  /// instantiated. Returns null if this class is not a template instantiation.
+  const CXXRecordDecl *getTemplateInstantiationPattern() const;
+
+  CXXRecordDecl *getTemplateInstantiationPattern() {
+    return const_cast<CXXRecordDecl *>(const_cast<const CXXRecordDecl *>(this)
+                                           ->getTemplateInstantiationPattern());
+  }
+
   /// \brief Returns the destructor decl for this class.
   CXXDestructorDecl *getDestructor() const;
 
   /// \brief If the class is a local class [class.local], returns
   /// the enclosing function declaration.
   const FunctionDecl *isLocalClass() const {
     if (const CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(getDeclContext()))
       return RD->isLocalClass();

lib/AST/DeclCXX.cpp

CXXRecordDecl::setTemplateSpecializationKind(TemplateSpecializationKind TSK) {
   if (MemberSpecializationInfo *MSInfo = getMemberSpecializationInfo()) {
     MSInfo->setTemplateSpecializationKind(TSK);
     return;
   }
   
   llvm_unreachable("Not a class template or member class specialization");
 }
 
+const CXXRecordDecl *CXXRecordDecl::getTemplateInstantiationPattern() const {
+  // If it's a class template specialization, find the template or partial
+  // specialization from which it was instantiated.
+  if (auto *TD = dyn_cast<ClassTemplateSpecializationDecl>(this)) {
+    auto From = TD->getInstantiatedFrom();
+    if (auto *CTD = From.dyn_cast<ClassTemplateDecl*>()) {
+      while (auto *NewCTD = CTD->getInstantiatedFromMemberTemplate()) {
+        if (NewCTD->isMemberSpecialization())
+          break;
+        CTD = NewCTD;
+      }
+      return CTD->getTemplatedDecl();
+    }
+    if (auto *CTPSD =
+            From.dyn_cast<ClassTemplatePartialSpecializationDecl *>()) {
+      while (auto *NewCTPSD = CTPSD->getInstantiatedFromMember()) {
+        if (NewCTPSD->isMemberSpecialization())
+          break;
+        CTPSD = NewCTPSD;
+      }
+      return CTPSD;
+    }
+  }
+
+  if (MemberSpecializationInfo *MSInfo = getMemberSpecializationInfo()) {
+    if (isTemplateInstantiation(MSInfo->getTemplateSpecializationKind())) {
+      const CXXRecordDecl *RD = this;
+      while (auto *NewRD = RD->getInstantiatedFromMemberClass())
+        RD = NewRD;
+      return RD;
+    }
+  }
+
+  assert(!isTemplateInstantiation(this->getTemplateSpecializationKind()) &&
+         "couldn't find pattern for class template instantiation");
+  return nullptr;
+}
+
 CXXDestructorDecl *CXXRecordDecl::getDestructor() const {
   ASTContext &Context = getASTContext();
   QualType ClassType = Context.getTypeDeclType(this);
 
   DeclarationName Name
     = Context.DeclarationNames.getCXXDestructorName(
                                           Context.getCanonicalType(ClassType));
 

lib/Sema/SemaLookup.cpp

 /// \brief Find the module in which the given declaration was defined.
 static Module *getDefiningModule(Decl *Entity) {
   if (FunctionDecl *FD = dyn_cast<FunctionDecl>(Entity)) {
     // If this function was instantiated from a template, the defining module is
     // the module containing the pattern.
     if (FunctionDecl *Pattern = FD->getTemplateInstantiationPattern())
       Entity = Pattern;
   } else if (CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(Entity)) {
-    // If it's a class template specialization, find the template or partial
-    // specialization from which it was instantiated.
-    if (ClassTemplateSpecializationDecl *SpecRD =
-            dyn_cast<ClassTemplateSpecializationDecl>(RD)) {
-      llvm::PointerUnion<ClassTemplateDecl*,
-                         ClassTemplatePartialSpecializationDecl*> From =
-          SpecRD->getInstantiatedFrom();
-      if (ClassTemplateDecl *FromTemplate = From.dyn_cast<ClassTemplateDecl*>())
-        Entity = FromTemplate->getTemplatedDecl();
-      else if (From)
-        Entity = From.get<ClassTemplatePartialSpecializationDecl*>();
-      // Otherwise, it's an explicit specialization.
-    } else if (MemberSpecializationInfo *MSInfo =
-                   RD->getMemberSpecializationInfo())
-      Entity = getInstantiatedFrom(RD, MSInfo);
+    if (CXXRecordDecl *Pattern = RD->getTemplateInstantiationPattern())
+      Entity = Pattern;
   } else if (EnumDecl *ED = dyn_cast<EnumDecl>(Entity)) {
     if (MemberSpecializationInfo *MSInfo = ED->getMemberSpecializationInfo())
       Entity = getInstantiatedFrom(ED, MSInfo);
   } else if (VarDecl *VD = dyn_cast<VarDecl>(Entity)) {
     // FIXME: Map from variable template specializations back to the template.
     if (MemberSpecializationInfo *MSInfo = VD->getMemberSpecializationInfo())
       Entity = getInstantiatedFrom(VD, MSInfo);
   }

lib/Sema/SemaType.cpp

 ///        in order to provide a definition of this entity.
 static bool hasVisibleDefinition(Sema &S, NamedDecl *D, NamedDecl **Suggested) {
   // Easy case: if we don't have modules, all declarations are visible.
   if (!S.getLangOpts().Modules)
     return true;
 
   // If this definition was instantiated from a template, map back to the
   // pattern from which it was instantiated.
-  //
-  // FIXME: There must be a better place for this to live.
   if (auto *RD = dyn_cast<CXXRecordDecl>(D)) {
-    if (auto *TD = dyn_cast<ClassTemplateSpecializationDecl>(RD)) {
-      auto From = TD->getInstantiatedFrom();
-      if (auto *CTD = From.dyn_cast<ClassTemplateDecl*>()) {
-        while (auto *NewCTD = CTD->getInstantiatedFromMemberTemplate()) {
-          if (NewCTD->isMemberSpecialization())
-            break;
-          CTD = NewCTD;
-        }
-        RD = CTD->getTemplatedDecl();
-      } else if (auto *CTPSD = From.dyn_cast<
-                     ClassTemplatePartialSpecializationDecl *>()) {
-        while (auto *NewCTPSD = CTPSD->getInstantiatedFromMember()) {
-          if (NewCTPSD->isMemberSpecialization())
-            break;
-          CTPSD = NewCTPSD;
-        }
-        RD = CTPSD;
-      }
-    } else if (isTemplateInstantiation(RD->getTemplateSpecializationKind())) {
-      while (auto *NewRD = RD->getInstantiatedFromMemberClass())
-        RD = NewRD;
-    }
+    if (auto *Pattern = RD->getTemplateInstantiationPattern())
+      RD = Pattern;
     D = RD->getDefinition();
   } else if (auto *ED = dyn_cast<EnumDecl>(D)) {
     while (auto *NewED = ED->getInstantiatedFromMemberEnum())
       ED = NewED;
     if (ED->isFixed()) {
       // If the enum has a fixed underlying type, any declaration of it will do.
       *Suggested = nullptr;
       for (auto *Redecl : ED->redecls()) {