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

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

Differential revision: https://reviews.llvm.org/D40621

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@319386 91177308-0d34-0410-b5e6-96231b3b80d8

Author: zmodem

lib/Sema/SemaTemplate.cpp

@@ -9239,10 +9239,18 @@ DeclResult Sema::ActOnExplicitInstantiation(Scope *S,
       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.

test/CodeGenCXX/dllimport.cpp

@@ -579,7 +579,7 @@ USE(inlineFuncTmpl<ExplicitDecl_Imported>)
 // 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()
@@ -609,6 +609,15 @@ USE(funcTmpl<ExplicitSpec_Imported>)
 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
 
 
 //===----------------------------------------------------------------------===//