A base subobject type doesn't make sense for unions; don't try to compute it. Based on patch by Yin Ma. Fixes PR11751.

llvm-svn: 148093

clang/lib/CodeGen/CGRecordLayoutBuilder.cpp

@@ -997,7 +997,7 @@ CGRecordLayout *CodeGenTypes::ComputeRecordLayout(const RecordDecl *D,
 
   // If we're in C++, compute the base subobject type.
   llvm::StructType *BaseTy = 0;
-  if (isa<CXXRecordDecl>(D)) {
+  if (isa<CXXRecordDecl>(D) && !D->isUnion()) {
     BaseTy = Builder.BaseSubobjectType;
     if (!BaseTy) BaseTy = Ty;
   }

clang/test/CodeGenCXX/empty-union.cpp

@@ -1,10 +1,7 @@
 // RUN: %clang_cc1 -emit-llvm -o - %s
 
 union sigval { };
+union sigval Test1;
 
-union sigval sigev_value;
-
-int main()
-{
-  return sizeof(sigev_value);
-}
+union NonPODUnion { ~NonPODUnion(); };
+union NonPODUnion Test2;