c++: support gcc's application of weak attribute on
class declaration which forces any such class and any 
class that inherits from such a class to have their 
typeinfo symbols be marked as weak.
// rdar://10246395
A    test/CodeGenCXX/weak-extern-typeinfo.cpp
M    lib/Sema/SemaDeclCXX.cpp
M    lib/Sema/SemaDeclAttr.cpp
M    lib/CodeGen/CGRTTI.cpp


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@142693 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/CGRTTI.cpp b/lib/CodeGen/CGRTTI.cpp
index 1b3cb08..d9790d0 100644
--- a/lib/CodeGen/CGRTTI.cpp
+++ b/lib/CodeGen/CGRTTI.cpp
@@ -336,6 +336,8 @@
 
     if (const RecordType *Record = dyn_cast<RecordType>(Ty)) {
       const CXXRecordDecl *RD = cast<CXXRecordDecl>(Record->getDecl());
+      if (RD->hasAttr<WeakAttr>())
+        return llvm::GlobalValue::WeakODRLinkage;
       if (RD->isDynamicClass())
         return CGM.getVTableLinkage(RD);
     }
diff --git a/lib/Sema/SemaDeclAttr.cpp b/lib/Sema/SemaDeclAttr.cpp
index b83b716..d801664 100644
--- a/lib/Sema/SemaDeclAttr.cpp
+++ b/lib/Sema/SemaDeclAttr.cpp
@@ -1914,6 +1914,10 @@
   }
 
   if (!isa<VarDecl>(D) && !isa<FunctionDecl>(D)) {
+    if (isa<CXXRecordDecl>(D)) {
+      D->addAttr(::new (S.Context) WeakAttr(Attr.getRange(), S.Context));
+      return;
+    }
     S.Diag(Attr.getLoc(), diag::warn_attribute_wrong_decl_type)
       << Attr.getName() << ExpectedVariableOrFunction;
     return;
diff --git a/lib/Sema/SemaDeclCXX.cpp b/lib/Sema/SemaDeclCXX.cpp
index f445e9f..2896e9f 100644
--- a/lib/Sema/SemaDeclCXX.cpp
+++ b/lib/Sema/SemaDeclCXX.cpp
@@ -1151,6 +1151,10 @@
       // Okay, add this new base class.
       KnownBaseTypes[NewBaseType] = Bases[idx];
       Bases[NumGoodBases++] = Bases[idx];
+      if (const RecordType *Record = dyn_cast<RecordType>(NewBaseType))
+        if (const CXXRecordDecl *RD = cast<CXXRecordDecl>(Record->getDecl()))
+          if (RD->hasAttr<WeakAttr>())
+            Class->addAttr(::new (Context) WeakAttr(SourceRange(), Context));
     }
   }