Index: cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
+++ cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
@@ -2863,6 +2863,9 @@
 def warn_attribute_dllexport_explicit_instantiation_decl : Warning<
   "explicit instantiation declaration should not be 'dllexport'">,
   InGroup<DiagGroup<"dllexport-explicit-instantiation-decl">>;
+def warn_attribute_dllexport_explicit_instantiation_def : Warning<
+  "'dllexport' attribute ignored on explicit instantiation definition">,
+  InGroup<IgnoredAttributes>;
 def warn_invalid_initializer_from_system_header : Warning<
   "invalid constructor form class in system header, should not be explicit">,
   InGroup<DiagGroup<"invalid-initializer-from-system-header">>;
Index: cfe/trunk/lib/Sema/SemaDeclCXX.cpp
===================================================================
--- cfe/trunk/lib/Sema/SemaDeclCXX.cpp
+++ cfe/trunk/lib/Sema/SemaDeclCXX.cpp
@@ -5697,9 +5697,11 @@
 
   TemplateSpecializationKind TSK = Class->getTemplateSpecializationKind();
 
-  // Ignore explicit dllexport on explicit class template instantiation declarations.
+  // Ignore explicit dllexport on explicit class template instantiation
+  // declarations, except in MinGW mode.
   if (ClassExported && !ClassAttr->isInherited() &&
-      TSK == TSK_ExplicitInstantiationDeclaration) {
+      TSK == TSK_ExplicitInstantiationDeclaration &&
+      !Context.getTargetInfo().getTriple().isWindowsGNUEnvironment()) {
     Class->dropAttr<DLLExportAttr>();
     return;
   }
Index: cfe/trunk/lib/Sema/SemaTemplate.cpp
===================================================================
--- cfe/trunk/lib/Sema/SemaTemplate.cpp
+++ cfe/trunk/lib/Sema/SemaTemplate.cpp
@@ -8732,8 +8732,10 @@
                                        ? TSK_ExplicitInstantiationDefinition
                                        : TSK_ExplicitInstantiationDeclaration;
 
-  if (TSK == TSK_ExplicitInstantiationDeclaration) {
-    // Check for dllexport class template instantiation declarations.
+  if (TSK == TSK_ExplicitInstantiationDeclaration &&
+      !Context.getTargetInfo().getTriple().isWindowsGNUEnvironment()) {
+    // Check for dllexport class template instantiation declarations,
+    // except for MinGW mode.
     for (const ParsedAttr &AL : Attr) {
       if (AL.getKind() == ParsedAttr::AT_DLLExport) {
         Diag(ExternLoc,
@@ -8793,6 +8795,19 @@
   TemplateSpecializationKind PrevDecl_TSK
     = PrevDecl ? PrevDecl->getTemplateSpecializationKind() : TSK_Undeclared;
 
+  if (TSK == TSK_ExplicitInstantiationDefinition && PrevDecl != nullptr &&
+      Context.getTargetInfo().getTriple().isWindowsGNUEnvironment()) {
+    // Check for dllexport class template instantiation definitions in MinGW
+    // mode, if a previous declaration of the instantiation was seen.
+    for (const ParsedAttr &AL : Attr) {
+      if (AL.getKind() == ParsedAttr::AT_DLLExport) {
+        Diag(AL.getLoc(),
+             diag::warn_attribute_dllexport_explicit_instantiation_def);
+        break;
+      }
+    }
+  }
+
   if (CheckExplicitInstantiation(*this, ClassTemplate, TemplateNameLoc,
                                  SS.isSet(), TSK))
     return true;
@@ -8949,6 +8964,14 @@
       dllExportImportClassTemplateSpecialization(*this, Def);
     }
 
+    // In MinGW mode, export the template instantiation if the declaration
+    // was marked dllexport.
+    if (PrevDecl_TSK == TSK_ExplicitInstantiationDeclaration &&
+        Context.getTargetInfo().getTriple().isWindowsGNUEnvironment() &&
+        PrevDecl->hasAttr<DLLExportAttr>()) {
+      dllExportImportClassTemplateSpecialization(*this, Def);
+    }
+
     // Set the template specialization kind. Make sure it is set before
     // instantiating the members which will trigger ASTConsumer callbacks.
     Specialization->setTemplateSpecializationKind(TSK);
Index: cfe/trunk/test/CodeGenCXX/mingw-template-dllexport.cpp
===================================================================
--- cfe/trunk/test/CodeGenCXX/mingw-template-dllexport.cpp
+++ cfe/trunk/test/CodeGenCXX/mingw-template-dllexport.cpp
@@ -0,0 +1,38 @@
+// RUN: %clang_cc1 -emit-llvm -triple i686-mingw32 %s -o - | FileCheck %s
+
+template <class T>
+class c {
+  void f();
+};
+
+template <class T> void c<T>::f() {}
+
+template class __declspec(dllexport) c<int>;
+
+// CHECK: define {{.*}} dllexport {{.*}} @_ZN1cIiE1fEv
+
+extern template class __declspec(dllexport) c<char>;
+template class c<char>;
+
+// CHECK: define {{.*}} dllexport {{.*}} @_ZN1cIcE1fEv
+
+extern template class c<double>;
+template class __declspec(dllexport) c<double>;
+
+// CHECK-NOT: define {{.*}} dllexport {{.*}} @_ZN1cIdE1fEv
+
+template <class T>
+struct outer {
+  void f();
+  struct inner {
+    void f();
+  };
+};
+
+template <class T> void outer<T>::f() {}
+template <class T> void outer<T>::inner::f() {}
+
+template class __declspec(dllexport) outer<int>;
+
+// CHECK: define {{.*}} dllexport {{.*}} @_ZN5outerIiE1fEv
+// CHECK-NOT: define {{.*}} dllexport {{.*}} @_ZN5outerIiE5inner1fEv
Index: cfe/trunk/test/SemaCXX/dllexport.cpp
===================================================================
--- cfe/trunk/test/SemaCXX/dllexport.cpp
+++ cfe/trunk/test/SemaCXX/dllexport.cpp
@@ -367,10 +367,16 @@
 
 // Don't instantiate class members of templates with explicit instantiation declarations, even if they are exported.
 struct IncompleteType2;
-template <typename T> struct __declspec(dllexport) ExportedTemplateWithExplicitInstantiationDecl { // expected-note{{attribute is here}}
+#ifdef MS
+// expected-note@+2{{attribute is here}}
+#endif
+template <typename T> struct __declspec(dllexport) ExportedTemplateWithExplicitInstantiationDecl {
   int f() { return sizeof(T); } // no-error
 };
-extern template struct ExportedTemplateWithExplicitInstantiationDecl<IncompleteType2>; // expected-warning{{explicit instantiation declaration should not be 'dllexport'}}
+#ifdef MS
+// expected-warning@+2{{explicit instantiation declaration should not be 'dllexport'}}
+#endif
+extern template struct ExportedTemplateWithExplicitInstantiationDecl<IncompleteType2>;
 
 // Instantiate class members for explicitly instantiated exported templates.
 struct IncompleteType3; // expected-note{{forward declaration of 'IncompleteType3'}}
@@ -402,10 +408,17 @@
 
 // Warn about explicit instantiation declarations of dllexport classes.
 template <typename T> struct ExplicitInstantiationDeclTemplate {};
-extern template struct __declspec(dllexport) ExplicitInstantiationDeclTemplate<int>; // expected-warning{{explicit instantiation declaration should not be 'dllexport'}} expected-note{{attribute is here}}
+#ifdef MS
+// expected-warning@+2{{explicit instantiation declaration should not be 'dllexport'}} expected-note@+2{{attribute is here}}
+#endif
+extern template struct __declspec(dllexport) ExplicitInstantiationDeclTemplate<int>;
 
-template <typename T> struct __declspec(dllexport) ExplicitInstantiationDeclExportedTemplate {}; // expected-note{{attribute is here}}
-extern template struct ExplicitInstantiationDeclExportedTemplate<int>; // expected-warning{{explicit instantiation declaration should not be 'dllexport'}}
+template <typename T> struct __declspec(dllexport) ExplicitInstantiationDeclExportedTemplate {};
+#ifdef MS
+// expected-note@-2{{attribute is here}}
+// expected-warning@+2{{explicit instantiation declaration should not be 'dllexport'}}
+#endif
+extern template struct ExplicitInstantiationDeclExportedTemplate<int>;
 
 namespace { struct InternalLinkageType {}; }
 struct __declspec(dllexport) PR23308 {
@@ -438,6 +451,12 @@
 template struct ExplicitlyInstantiatedTemplate<int>;
 template <typename T> struct ExplicitlyExportInstantiatedTemplate { void func() {} };
 template struct __declspec(dllexport) ExplicitlyExportInstantiatedTemplate<int>;
+template <typename T> struct ExplicitlyExportDeclaredInstantiatedTemplate { void func() {} };
+extern template struct ExplicitlyExportDeclaredInstantiatedTemplate<int>;
+#ifndef MS
+// expected-warning@+2{{'dllexport' attribute ignored on explicit instantiation definition}}
+#endif
+template struct __declspec(dllexport) ExplicitlyExportDeclaredInstantiatedTemplate<int>;
 template <typename T> struct ExplicitlyImportInstantiatedTemplate { void func() {} };
 template struct __declspec(dllimport) ExplicitlyImportInstantiatedTemplate<int>;