Fix PR8796.

The problem was that we were asserting the we never added an empty class
to the same offset twice. This is not true for unions, where two members, empty
or not, can have the some offset.

llvm-svn: 122633

clang/lib/AST/RecordLayoutBuilder.cpp

@@ -216,10 +216,12 @@ void EmptySubobjectMap::AddSubobjectAtOffset(const CXXRecordDecl *RD,
   if (!RD->isEmpty())
     return;
 
+  // If we have empty structures inside an union, we can assign both
+  // the same offset. Just avoid pushing them twice in the list.
   ClassVectorTy& Classes = EmptyClassOffsets[Offset];
-  assert(std::find(Classes.begin(), Classes.end(), RD) == Classes.end() &&
-         "Duplicate empty class detected!");
-
+  if (std::find(Classes.begin(), Classes.end(), RD) != Classes.end())
+    return;
+  
   Classes.push_back(RD);
   
   // Update the empty class offset.

clang/test/CodeGenCXX/empty-classes.cpp

@@ -53,6 +53,19 @@ int f() {
   return 0;
 }
 
+namespace PR8796 {
+  struct FreeCell {
+  };
+  union ThingOrCell {
+    FreeCell t;
+    FreeCell cell;
+  };
+  struct Things {
+    ThingOrCell things;
+  };
+  Things x;
+}
+
 #ifdef HARNESS
 extern "C" void printf(const char *, ...);