[Clang] Apply exclude_from_explicit_instantiation to dllimport/dllexport

Attaching `__declspec(dllexport/dllimport)` to explicit instantiation
declaration made its whole member instantiated even if they were
`__attribute__((__exclude_from_explicit_instantation__))`.
Such members should not be instantiated nor be exported to avoid
symbol leakage or duplication.

Author: kikairoya

clang/lib/Sema/SemaDeclCXX.cpp

@@ -6551,6 +6551,8 @@ void Sema::checkClassLevelDLLAttribute(CXXRecordDecl *Class) {
     return;
   }
 
+  TemplateSpecializationKind TSK = Class->getTemplateSpecializationKind();
+
   if (Context.getTargetInfo().shouldDLLImportComdatSymbols() &&
       !ClassAttr->isInherited()) {
     // Diagnose dll attributes on members of class with dll attribute.
@@ -6561,6 +6563,11 @@ void Sema::checkClassLevelDLLAttribute(CXXRecordDecl *Class) {
       if (!MemberAttr || MemberAttr->isInherited() || Member->isInvalidDecl())
         continue;
 
+      if ((TSK == TSK_ExplicitInstantiationDeclaration ||
+           TSK == TSK_ExplicitInstantiationDefinition) &&
+          Member->hasAttr<ExcludeFromExplicitInstantiationAttr>())
+        continue;
+
       Diag(MemberAttr->getLocation(),
              diag::err_attribute_dll_member_of_dll_class)
           << MemberAttr << ClassAttr;
@@ -6583,8 +6590,6 @@ void Sema::checkClassLevelDLLAttribute(CXXRecordDecl *Class) {
       !ClassExported &&
       cast<DLLImportAttr>(ClassAttr)->wasPropagatedToBaseTemplate();
 
-  TemplateSpecializationKind TSK = Class->getTemplateSpecializationKind();
-
   // Ignore explicit dllexport on explicit class template instantiation
   // declarations, except in MinGW mode.
   if (ClassExported && !ClassAttr->isInherited() &&
@@ -6601,6 +6606,11 @@ void Sema::checkClassLevelDLLAttribute(CXXRecordDecl *Class) {
   // seem to be true in practice?
 
   for (Decl *Member : Class->decls()) {
+    if ((TSK == TSK_ExplicitInstantiationDeclaration ||
+         TSK == TSK_ExplicitInstantiationDefinition) &&
+        Member->hasAttr<ExcludeFromExplicitInstantiationAttr>())
+      continue;
+
     VarDecl *VD = dyn_cast<VarDecl>(Member);
     CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(Member);