MS ABI: Treat explicit instantiation definitions of dllimport function templates as explicit instantiation decls (PR35435)

[hans]

Summary

This matches MSVC's behaviour, and we already do it for class templates since r270897.

[rnk]

Looks good, thanks!

[zahiraam]

Looks good to me 2.

lib/Sema/SemaTemplate.cpp

if (CheckSpecializationInstantiationRedecl(D.getIdentifierLoc(), TSK,
       return true;
 
     // FIXME: We may still want to build some representation of this
     // explicit specialization.
     if (HasNoEffect)
       return (Decl*) nullptr;
   }
 
-  Specialization->setTemplateSpecializationKind(TSK, D.getIdentifierLoc());
   if (Attr)
     ProcessDeclAttributeList(S, Specialization, Attr);
 
+  // In MSVC mode, dllimported explicit instantiation definitions are treated as
+  // instantiation declarations.
+  if (TSK == TSK_ExplicitInstantiationDefinition &&
+      Specialization->hasAttr<DLLImportAttr>() &&
+      Context.getTargetInfo().getCXXABI().isMicrosoft())
+    TSK = TSK_ExplicitInstantiationDeclaration;
+
+  Specialization->setTemplateSpecializationKind(TSK, D.getIdentifierLoc());
+
   if (Specialization->isDefined()) {
     // Let the ASTConsumer know that this function has been explicitly
     // instantiated now, and its linkage might have changed.
     Consumer.HandleTopLevelDecl(DeclGroupRef(Specialization));
   } else if (TSK == TSK_ExplicitInstantiationDefinition)
     InstantiateFunctionDefinition(D.getIdentifierLoc(), Specialization);
 
   // C++0x [temp.explicit]p2:

test/CodeGenCXX/dllimport.cpp

 USE(inlineFuncTmpl<ExplicitDecl_Imported>)
 
 
 // Import explicit instantiation definition of a non-imported function template.
 // MSC-DAG: declare dllimport void @"\01??$funcTmpl@UExplicitInst_Imported@@@@YAXXZ"()
 // MSC-DAG: declare dllimport void @"\01??$inlineFuncTmpl@UExplicitInst_Imported@@@@YAXXZ"()
 // GNU-DAG: declare dllimport void @_Z8funcTmplI21ExplicitInst_ImportedEvv()
 // GNU-DAG: define weak_odr void @_Z14inlineFuncTmplI21ExplicitInst_ImportedEvv()
-// MO1-DAG: define available_externally dllimport void @"\01??$funcTmpl@UExplicitInst_Imported@@@@YAXXZ"()
+// MO1-DAG: declare dllimport void @"\01??$funcTmpl@UExplicitInst_Imported@@@@YAXXZ"()
 // MO1-DAG: define available_externally dllimport void @"\01??$inlineFuncTmpl@UExplicitInst_Imported@@@@YAXXZ"()
 // GO1-DAG: define available_externally dllimport void @_Z8funcTmplI21ExplicitInst_ImportedEvv()
 // GO1-DAG: define weak_odr void @_Z14inlineFuncTmplI21ExplicitInst_ImportedEvv()
 template __declspec(dllimport) void funcTmpl<ExplicitInst_Imported>();
 template __declspec(dllimport) void inlineFuncTmpl<ExplicitInst_Imported>();
 USE(funcTmpl<ExplicitInst_Imported>)
 USE(inlineFuncTmpl<ExplicitInst_Imported>)
 

 
 // MSC-DAG: declare dllimport void @"\01??$funcTmpl@UExplicitSpec_InlineDef_Imported@@@@YAXXZ"()
 // GNU-DAG: define linkonce_odr void @_Z8funcTmplI31ExplicitSpec_InlineDef_ImportedEvv()
 // MO1-DAG: define available_externally dllimport void @"\01??$funcTmpl@UExplicitSpec_InlineDef_Imported@@@@YAXXZ"()
 // GO1-DAG: define linkonce_odr void @_Z8funcTmplI31ExplicitSpec_InlineDef_ImportedEvv()
 template<> __declspec(dllimport) inline void funcTmpl<ExplicitSpec_InlineDef_Imported>() {}
 USE(funcTmpl<ExplicitSpec_InlineDef_Imported>)
 
+#ifdef MSABI
+namespace pr35435 {
+struct X;
+template <typename T> struct __declspec(dllimport) S {
+  void foo(T *t) { t->problem(); }
+};
+template void S<X>::foo(X*); // Cannot be instantiated because X is incomplete; dllimport means it's treated as an instantiation decl.
+}
+#endif
 
 
 //===----------------------------------------------------------------------===//
 // Classes
 //===----------------------------------------------------------------------===//
 
 struct __declspec(dllimport) T {
   void a() {}