[MinGW] Fix dllexport of explicit template instantiation

[mstorsjo]

Summary

Contrary to MSVC, GCC/MinGW needs to have the dllexport attribute on the template instantiation declaration, not on the definition.

Previously clang never marked explicit template instantiations as dllexport in MinGW mode, if the instantiation had a previous declaration, regardless of where the attribute was placed. This makes Clang behave like GCC in this regard, and allows using the same attribute form for both MinGW compilers.

This fixes PR40256.

[smeenai]

LGTM, though I'd wait for Hans and/or Reid too.

I like the GCC/MinGW behavior here much more than the MSVC behavior. Having to mark the definitions only in the explicit instantiations case (for MSVC) whereas everything else requires you to mark the declarations is a weird inconsistency.

[hans]

Looks good to me.

[mstorsjo]

Adjusted the patch to not warn if there is no previous declaration of the instantiation, allowing the dllexport attribute on the definition in that case.

cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td

 def err_attribute_dllimport_static_field_definition : Error<
   "definition of dllimport static field not allowed">;
 def warn_attribute_dllimport_static_field_definition : Warning<
   "definition of dllimport static field">,
   InGroup<DiagGroup<"dllimport-static-field-def">>;
 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">>;
 def note_used_in_initialization_here : Note<"used in initialization here">;
 def err_attribute_dll_member_of_dll_class : Error<
   "attribute %q0 cannot be applied to member of %q1 class">;
 def warn_attribute_dll_instantiated_base_class : Warning<
   "propagating dll attribute to %select{already instantiated|explicitly specialized}0 "

cfe/trunk/lib/Sema/SemaDeclCXX.cpp

void Sema::checkClassLevelDLLAttribute(CXXRecordDecl *Class) {
   // a base class template specialization. We don't apply these attributes to
   // static data members.
   const bool PropagatedImport =
       !ClassExported &&
       cast<DLLImportAttr>(ClassAttr)->wasPropagatedToBaseTemplate();
 
   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;
   }
 
   // Force declaration of implicit members so they can inherit the attribute.
   ForceDeclarationOfImplicitMembers(Class);
 
   // FIXME: MSVC's docs say all bases must be exportable, but this doesn't

cfe/trunk/lib/Sema/SemaTemplate.cpp

DeclResult Sema::ActOnExplicitInstantiation(
   // C++0x [temp.explicit]p2:
   //   There are two forms of explicit instantiation: an explicit instantiation
   //   definition and an explicit instantiation declaration. An explicit
   //   instantiation declaration begins with the extern keyword. [...]
   TemplateSpecializationKind TSK = ExternLoc.isInvalid()
                                        ? 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,
              diag::warn_attribute_dllexport_explicit_instantiation_decl);
         Diag(AL.getLoc(), diag::note_attribute);
         break;
       }
     }
DeclResult Sema::ActOnExplicitInstantiation(
   // corresponds to these arguments.
   void *InsertPos = nullptr;
   ClassTemplateSpecializationDecl *PrevDecl
     = ClassTemplate->findSpecialization(Converted, InsertPos);
 
   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;
 
   ClassTemplateSpecializationDecl *Specialization = nullptr;
 
   bool HasNoEffect = false;
   if (PrevDecl) {
if (Old_TSK == TSK_ImplicitInstantiation && NewlyDLLExported &&
       // attribute, since the Def and Specialization will be the same in the
       // case of Old_TSK == TSK_ImplicitInstantiation, and we already added the
       // attribute to the Specialization; we just need to make it take effect.
       assert(Def == Specialization &&
              "Def and Specialization should match for implicit instantiation");
       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);
     InstantiateClassTemplateSpecializationMembers(TemplateNameLoc, Def, TSK);
   } else {
 
     // Set the template specialization kind.
     Specialization->setTemplateSpecializationKind(TSK);

cfe/trunk/test/CodeGenCXX/mingw-template-dllexport.cpp

+// 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

cfe/trunk/test/SemaCXX/dllexport.cpp

 struct IncompleteType;
 template <typename T> struct __declspec(dllexport) ImplicitlyInstantiatedExportedTemplate {
   int f() { return sizeof(T); } // no-error
 };
 ImplicitlyInstantiatedExportedTemplate<IncompleteType> implicitlyInstantiatedExportedTemplate;
 
 // 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'}}
 template <typename T> struct __declspec(dllexport) ExplicitlyInstantiatedExportedTemplate {
   int f() { return sizeof(T); } // expected-error{{invalid application of 'sizeof' to an incomplete type 'IncompleteType3'}}
 };
 template struct ExplicitlyInstantiatedExportedTemplate<IncompleteType3>; // expected-note{{in instantiation of member function 'ExplicitlyInstantiatedExportedTemplate<IncompleteType3>::f' requested here}}
 

 struct IncompleteType5;
 template <typename T> struct __declspec(dllexport) ExportedBaseClassTemplateOfExportedClass {
   int f() { return sizeof(T); }; // no-error
 };
 struct __declspec(dllexport) ExportedBaseClass2 : public ExportedBaseClassTemplateOfExportedClass<IncompleteType5> {};
 
 // 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 {
   void f(InternalLinkageType*);
 };
 void PR23308::f(InternalLinkageType*) {} // No error; we don't try to export f because it has internal linkage.
 
 //===----------------------------------------------------------------------===//

 
 template <typename T> struct ExplicitlyInstantiatedTemplate { void func() {} };
 #ifdef MS
 // expected-note@+2{{class template 'ExplicitlyInstantiatedTemplate<int>' was instantiated here}}
 #endif
 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>;
 
 // ClassTemplate<int> gets exported.
 class __declspec(dllexport) DerivedFromTemplate : public ClassTemplate<int> {};
 
 // ClassTemplate<int> is already exported.
 class __declspec(dllexport) DerivedFromTemplate2 : public ClassTemplate<int> {};