1 files changed, 50 insertions, 28 deletions

diff --git a/lib/Sema/SemaDeclCXX.cpp b/lib/Sema/SemaDeclCXX.cpp
index 29455087ae..1c0a72bf11 100644
--- a/lib/Sema/SemaDeclCXX.cpp
+++ b/lib/Sema/SemaDeclCXX.cpp
@@ -1753,38 +1753,67 @@ struct BaseAndFieldInfo {
 };
 }
 
+static void RecordFieldInitializer(BaseAndFieldInfo &Info,
+                                   FieldDecl *Top, FieldDecl *Field,
+                                   CXXBaseOrMemberInitializer *Init) {
+  // If the member doesn't need to be initialized, Init will still be null.
+  if (!Init)
+    return;
+
+  Info.AllToInit.push_back(Init);
+  if (Field != Top) {
+    Init->setMember(Top);
+    Init->setAnonUnionMember(Field);
+  }
+}
+
 static bool CollectFieldInitializer(BaseAndFieldInfo &Info,
                                     FieldDecl *Top, FieldDecl *Field) {
 
-  // Overwhelmingly common case:  we have a direct initializer for this field.
+  // Overwhelmingly common case: we have a direct initializer for this field.
   if (CXXBaseOrMemberInitializer *Init = Info.AllBaseFields.lookup(Field)) {
-    Info.AllToInit.push_back(Init);
-
-    if (Field != Top) {
-      Init->setMember(Top);
-      Init->setAnonUnionMember(Field);
-    }
+    RecordFieldInitializer(Info, Top, Field, Init);
     return false;
   }
 
   if (Info.IIK == IIK_Default && Field->isAnonymousStructOrUnion()) {
     const RecordType *FieldClassType = Field->getType()->getAs<RecordType>();
     assert(FieldClassType && "anonymous struct/union without record type");
-
-    // Walk through the members, tying in any initializers for fields
-    // we find.  The earlier semantic checks should prevent redundant
-    // initialization of union members, given the requirement that
-    // union members never have non-trivial default constructors.
-
-    // TODO: in C++0x, it might be legal to have union members with
-    // non-trivial default constructors in unions.  Revise this
-    // implementation then with the appropriate semantics.
     CXXRecordDecl *FieldClassDecl
       = cast<CXXRecordDecl>(FieldClassType->getDecl());
-    for (RecordDecl::field_iterator FA = FieldClassDecl->field_begin(),
-           EA = FieldClassDecl->field_end(); FA != EA; FA++)
-      if (CollectFieldInitializer(Info, Top, *FA))
-        return true;
+
+    // Even though union members never have non-trivial default
+    // constructions in C++03, we still build member initializers for aggregate
+    // record types which can be union members, and C++0x allows non-trivial
+    // default constructors for union members, so we ensure that only one
+    // member is initialized for these.
+    if (FieldClassDecl->isUnion()) {
+      // First check for an explicit initializer for one field.
+      for (RecordDecl::field_iterator FA = FieldClassDecl->field_begin(),
+           EA = FieldClassDecl->field_end(); FA != EA; FA++) {
+        if (CXXBaseOrMemberInitializer *Init = Info.AllBaseFields.lookup(*FA)) {
+          RecordFieldInitializer(Info, Top, *FA, Init);
+
+          // Once we've initialized a field of an anonymous union, the union
+          // field in the class is also initialized, so exit immediately.
+          return false;
+        }
+      }
+
+      // Fallthrough and construct a default initializer for the union as
+      // a whole, which can call its default constructor if such a thing exists
+      // (C++0x perhaps). FIXME: It's not clear that this is the correct
+      // behavior going forward with C++0x, when anonymous unions there are
+      // finalized, we should revisit this.
+    } else {
+      // For structs, we simply descend through to initialize all members where
+      // necessary.
+      for (RecordDecl::field_iterator FA = FieldClassDecl->field_begin(),
+           EA = FieldClassDecl->field_end(); FA != EA; FA++) {
+        if (CollectFieldInitializer(Info, Top, *FA))
+          return true;
+      }
+    }
   }
 
   // Don't try to build an implicit initializer if there were semantic
@@ -1796,15 +1825,8 @@ static bool CollectFieldInitializer(BaseAndFieldInfo &Info,
   CXXBaseOrMemberInitializer *Init = 0;
   if (BuildImplicitMemberInitializer(Info.S, Info.Ctor, Info.IIK, Field, Init))
     return true;
-    
-  // If the member doesn't need to be initialized, Init will still be null.
-  if (!Init) return false;
 
-  Info.AllToInit.push_back(Init);
-  if (Top != Field) {
-    Init->setMember(Top);
-    Init->setAnonUnionMember(Field);
-  }
+  RecordFieldInitializer(Info, Top, Field, Init);
   return false;
 }