Narrow the -Wunsupported-dll-base-class-template warning.

Don't warn about not being able to propagate dll attribute to a base class template
when that base already has a different attribute.

MSVC doesn't actually try to do this; the first attribute that was propagated
takes precedence, so Clang is already doing the right thing and there's no
need to warn.

(This is a step towards fixing PR21718.)

llvm-svn: 239372

1 files changed, 8 insertions, 16 deletions

diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index b1dfe0e95e2..b67dfb8e342 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -1364,26 +1364,18 @@ static void propagateDLLAttrToBaseClassTemplate(
     return;
   }
 
-  bool DifferentAttribute = false;
-  if (Attr *SpecializationAttr = getDLLAttr(BaseTemplateSpec)) {
-    if (!SpecializationAttr->isInherited()) {
-      // The template has previously been specialized or instantiated with an
-      // explicit attribute. We should not try to change it.
-      return;
-    }
-    if (SpecializationAttr->getKind() == ClassAttr->getKind()) {
-      // The specialization already has the right attribute.
-      return;
-    }
-    DifferentAttribute = true;
+  if (getDLLAttr(BaseTemplateSpec)) {
+    // The template has already been specialized or instantiated with an
+    // attribute, explicitly or through propagation. We should not try to change
+    // it.
+    return;
   }
 
   // The template was previously instantiated or explicitly specialized without
-  // a dll attribute, or the template was previously instantiated with a
-  // different inherited attribute. It's too late for us to change the
-  // attribute, so warn that this is unsupported.
+  // a dll attribute, It's too late for us to add an attribute, so warn that
+  // this is unsupported.
   S.Diag(BaseLoc, diag::warn_attribute_dll_instantiated_base_class)
-      << BaseTemplateSpec->isExplicitSpecialization() << DifferentAttribute;
+      << BaseTemplateSpec->isExplicitSpecialization();
   S.Diag(ClassAttr->getLocation(), diag::note_attribute);
   if (BaseTemplateSpec->isExplicitSpecialization()) {
     S.Diag(BaseTemplateSpec->getLocation(),