[macho2yaml] Don't write empty linkedit data

Since I stopped writing empty export tries it causes LinkEdit to potentially be completely empty which results in invalid yaml being generated.

To prevent this we skip linkedit data if it is empty.

llvm-svn: 278985

llvm/include/llvm/ObjectYAML/MachOYAML.h

@@ -100,6 +100,8 @@ struct LinkEditData {
   MachOYAML::ExportEntry ExportTrie;
   std::vector<NListEntry> NameList;
   std::vector<StringRef> StringTable;
+
+  bool isEmpty() const;
 };
 
 struct Object {

llvm/lib/ObjectYAML/MachOYAML.cpp

@@ -22,6 +22,10 @@ namespace llvm {
 
 MachOYAML::LoadCommand::~LoadCommand() {}
 
+bool MachOYAML::LinkEditData::isEmpty() const {
+  return 0 == RebaseOpcodes.size() + BindOpcodes.size() + WeakBindOpcodes.size() + LazyBindOpcodes.size() + ExportTrie.Children.size() + NameList.size() + StringTable.size();
+}
+
 namespace yaml {
 
 void ScalarTraits<char_16>::output(const char_16 &Val, void *,
@@ -95,7 +99,8 @@ void MappingTraits<MachOYAML::Object>::mapping(IO &IO,
   IO.mapTag("!mach-o", true);
   IO.mapRequired("FileHeader", Object.Header);
   IO.mapOptional("LoadCommands", Object.LoadCommands);
-  IO.mapOptional("LinkEditData", Object.LinkEdit);
+  if(!Object.LinkEdit.isEmpty() || !IO.outputting())
+    IO.mapOptional("LinkEditData", Object.LinkEdit);
 
   if (IO.getContext() == &Object)
     IO.setContext(nullptr);

llvm/test/ObjectYAML/MachO/bogus_load_command.yaml

@@ -49,3 +49,4 @@ LoadCommands:
 #CHECK:       - 0x0A
 #CHECK:       - 0x0B
 #CHECK:       - 0x0C
+#CHECK-NOT: LinkEditData: