Index: clang/lib/AST/Decl.cpp
===================================================================
--- clang/lib/AST/Decl.cpp
+++ clang/lib/AST/Decl.cpp
@@ -486,6 +486,12 @@
   if (considerVisibility)
     LV.mergeVisibility(argsLV);
   LV.mergeExternalVisibility(argsLV);
+
+  // MSVC forces external linkage for explicit instantiations of template
+  // classes with dllexport/dllimport attributes.
+  if (spec->getASTContext().getTargetInfo().shouldDLLImportComdatSymbols())
+    if (spec->hasAttr<DLLExportAttr>() || spec->hasAttr<DLLImportAttr>())
+      LV.setLinkage(Linkage::ExternalLinkage);
 }
 
 /// Should we consider visibility associated with the template
@@ -1346,6 +1352,15 @@
   }
 
   ASTContext &Context = D->getASTContext();
+
+  // MSVC allows dllexport/llimport on local classes and imparts external
+  // linkage to them.
+  if (Context.getTargetInfo().shouldDLLImportComdatSymbols()) {
+    if (const auto *Record = dyn_cast<CXXRecordDecl>(D))
+      if (Record->hasAttr<DLLExportAttr>() || Record->hasAttr<DLLImportAttr>())
+        return LinkageInfo();
+  }
+
   if (!Context.getLangOpts().CPlusPlus)
     return LinkageInfo::none();
 
Index: clang/test/SemaCXX/dllexport.cpp
===================================================================
--- clang/test/SemaCXX/dllexport.cpp
+++ clang/test/SemaCXX/dllexport.cpp
@@ -434,7 +434,16 @@
 // Classes with template base classes
 //===----------------------------------------------------------------------===//
 
+class Base {};
+class __declspec(dllexport) ExportedClass {};
+class __declspec(dllimport) ImportedClass {};
+
 template <typename T> class ClassTemplate {};
+#if not defined(MS) && not defined(WI)
+// expected-error@+4{{'ExportedClassTemplate<LocalCRTP>' must have external linkage when declared 'dllexport'}}
+// expected-error@+3{{'ExportedClassTemplate<ExportedLocalDerivedFromExportedTemplateCRTP>' must have external linkage when declared 'dllexport'}}
+// expected-error@+3{{'ImportedClassTemplate<ExportedLocalDerivedFromImportedTemplateCRTP>' must have external linkage when declared 'dllimport'}}
+#endif
 template <typename T> class __declspec(dllexport) ExportedClassTemplate {};
 template <typename T> class __declspec(dllimport) ImportedClassTemplate {};
 
@@ -516,6 +525,44 @@
 extern template struct ExplicitInstantiationDeclTemplateBase<int>;
 struct __declspec(dllexport) DerivedFromExplicitInstantiationDeclTemplateBase : public ExplicitInstantiationDeclTemplateBase<int> {};
 
+void func() {
+  // MSVC propagates dllexport to derived classes even if they don't have external linkage.
+  class LocalDerivedFromExportedClass : public ExportedClass {};
+  class LocalDerivedFromExportedTemplate : public ExportedClassTemplate<int> {};
+#if not defined(MS) && not defined (WI)
+  // expected-note@+2{{in instantiation of template class 'ExportedClassTemplate<LocalCRTP>' requested here}}
+#endif
+  class LocalCRTP : public ExportedClassTemplate<LocalCRTP> {};
+  // MSVC allows exported classes in a local context.
+#if not defined(MS) && not defined (WI)
+  // expected-error@+10{{'ExportedLocalDerivedFromBase' must have external linkage when declared 'dllexport'}}
+  // expected-error@+10{{'ExportedLocalDerivedFromTemplate' must have external linkage when declared 'dllexport'}}
+  // expected-error@+10{{'ExportedLocalDerivedFromExportedClass' must have external linkage when declared 'dllexport'}}
+  // expected-error@+10{{'ExportedLocalDerivedFromImportedClass' must have external linkage when declared 'dllexport'}}
+  // expected-error@+10{{'ExportedLocalDerivedFromExportedTemplate' must have external linkage when declared 'dllexport'}}
+  // expected-error@+10{{'ExportedLocalDerivedFromImportedTemplate' must have external linkage when declared 'dllexport'}}
+  // expected-error@+10{{'ExportedLocalCRTP' must have external linkage when declared 'dllexport'}}
+  // expected-error@+10{{'ExportedLocalDerivedFromExportedTemplateCRTP' must have external linkage when declared 'dllexport'}}
+  // expected-error@+14{{'ExportedLocalDerivedFromImportedTemplateCRTP' must have external linkage when declared 'dllexport'}}
+#endif
+  class __declspec(dllexport) ExportedLocalDerivedFromBase : public Base {};
+  class __declspec(dllexport) ExportedLocalDerivedFromTemplate : public ClassTemplate<int> {};
+  class __declspec(dllexport) ExportedLocalDerivedFromExportedClass : public ExportedClass {};
+  class __declspec(dllexport) ExportedLocalDerivedFromImportedClass : public ImportedClass {};
+  class __declspec(dllexport) ExportedLocalDerivedFromExportedTemplate : public ExportedClassTemplate<int> {};
+  class __declspec(dllexport) ExportedLocalDerivedFromImportedTemplate : public ImportedClassTemplate<int> {};
+  class __declspec(dllexport) ExportedLocalCRTP : public ClassTemplate<ExportedLocalCRTP> {};
+  class __declspec(dllexport) ExportedLocalDerivedFromExportedTemplateCRTP :
+#if not defined(MS) && not defined (WI)
+  // expected-note@+2{{in instantiation of template class 'ExportedClassTemplate<ExportedLocalDerivedFromExportedTemplateCRTP>' requested here}}
+#endif
+    public ExportedClassTemplate<ExportedLocalDerivedFromExportedTemplateCRTP> {};
+  class __declspec(dllexport) ExportedLocalDerivedFromImportedTemplateCRTP :
+#if not defined(MS) && not defined (WI)
+  // expected-note@+2{{in instantiation of template class 'ImportedClassTemplate<ExportedLocalDerivedFromImportedTemplateCRTP>' requested here}}
+#endif
+    public ImportedClassTemplate<ExportedLocalDerivedFromImportedTemplateCRTP> {};
+}
 
 //===----------------------------------------------------------------------===//
 // Precedence
Index: clang/test/SemaCXX/dllimport.cpp
===================================================================
--- clang/test/SemaCXX/dllimport.cpp
+++ clang/test/SemaCXX/dllimport.cpp
@@ -228,7 +228,6 @@
 
 template<typename T> __declspec(dllimport) auto InternalAutoTypeVarTmpl = Internal(); // expected-error{{definition of dllimport data}} // expected-error{{'InternalAutoTypeVarTmpl' must have external linkage when declared 'dllimport'}}
 
-
 template<typename T> int VarTmpl;
 template<typename T> __declspec(dllimport) int ImportedVarTmpl;
 
@@ -1528,8 +1527,19 @@
 // Classes with template base classes
 //===----------------------------------------------------------------------===//
 
+class Base {};
+class __declspec(dllexport) ExportedClass {};
+class __declspec(dllimport) ImportedClass {};
+
+#ifdef GNU
+// expected-error@+2{{'ExportedClassTemplate<ImportedLocalDerivedFromExportedTemplateCRTP>' must have external linkage when declared 'dllexport'}}
+#endif
 template <typename T> class __declspec(dllexport) ExportedClassTemplate {};
 
+#ifdef GNU
+// expected-error@+3{{'ImportedClassTemplate<LocalCRTP>' must have external linkage when declared 'dllimport'}}
+// expected-error@+2{{'ImportedClassTemplate<ImportedLocalDerivedFromImportedTemplateCRTP>' must have external linkage when declared 'dllimport'}}
+#endif
 template <typename T> class __declspec(dllimport) ImportedClassTemplate {};
 
 // ClassTemplate<int> gets imported.
@@ -1604,6 +1614,41 @@
 extern template struct ExplicitInstantiationDeclTemplateBase<int>;
 struct __declspec(dllimport) DerivedFromExplicitInstantiationDeclTemplateBase : public ExplicitInstantiationDeclTemplateBase<int> {};
 
+void func() {
+  // MSVC propagates dllimport to derived classes even if they don't have external linkage.
+  class LocalDerivedFromImportedClass : public ImportedClass {};
+  class LocalDerivedFromImportedTemplate : public ImportedClassTemplate<int> {};
+#ifdef GNU
+  // expected-note@+2{{in instantiation of template class 'ImportedClassTemplate<LocalCRTP>' requested here}}
+#endif
+  class LocalCRTP : public ImportedClassTemplate<LocalCRTP> {};
+  // MSVC allows imported classes in a local context.
+#ifdef GNU
+  // expected-error@+12{{'ImportedLocalDerivedFromBase' must have external linkage when declared 'dllimport'}}
+  // expected-error@+12{{'ImportedLocalDerivedFromTemplate' must have external linkage when declared 'dllimport'}}
+  // expected-error@+12{{'ImportedLocalDerivedFromExportedClass' must have external linkage when declared 'dllimport'}}
+  // expected-error@+12{{'ImportedLocalDerivedFromImportedClass' must have external linkage when declared 'dllimport'}}
+  // expected-error@+12{{'ImportedLocalDerivedFromExportedTemplate' must have external linkage when declared 'dllimport'}}
+  // expected-error@+12{{'ImportedLocalDerivedFromImportedTemplate' must have external linkage when declared 'dllimport'}}
+  // expected-error@+12{{'ImportedLocalCRTP' must have external linkage when declared 'dllimport'}}
+  // expected-error@+12{{'ImportedLocalDerivedFromExportedTemplateCRTP' must have external linkage when declared 'dllimport'}}
+  // expected-error@+13{{'ImportedLocalDerivedFromImportedTemplateCRTP' must have external linkage when declared 'dllimport'}}
+  // expected-note@+11{{in instantiation of template class 'ExportedClassTemplate<ImportedLocalDerivedFromExportedTemplateCRTP>' requested here}}
+  // expected-note@+12{{in instantiation of template class 'ImportedClassTemplate<ImportedLocalDerivedFromImportedTemplateCRTP>' requested here}}
+#endif
+  class __declspec(dllimport) ImportedLocalDerivedFromBase : public Base {};
+  class __declspec(dllimport) ImportedLocalDerivedFromTemplate : public ClassTemplate<int> {};
+  class __declspec(dllimport) ImportedLocalDerivedFromExportedClass : public ExportedClass {};
+  class __declspec(dllimport) ImportedLocalDerivedFromImportedClass : public ImportedClass {};
+  class __declspec(dllimport) ImportedLocalDerivedFromExportedTemplate : public ExportedClassTemplate<int> {};
+  class __declspec(dllimport) ImportedLocalDerivedFromImportedTemplate : public ImportedClassTemplate<int> {};
+  class __declspec(dllimport) ImportedLocalCRTP : public ClassTemplate<ImportedLocalCRTP> {};
+  class __declspec(dllimport) ImportedLocalDerivedFromExportedTemplateCRTP :
+    public ExportedClassTemplate<ImportedLocalDerivedFromExportedTemplateCRTP> {};
+  class __declspec(dllimport) ImportedLocalDerivedFromImportedTemplateCRTP :
+    public ImportedClassTemplate<ImportedLocalDerivedFromImportedTemplateCRTP> {};
+}
+
 //===----------------------------------------------------------------------===//
 // Lambdas
 //===----------------------------------------------------------------------===//