Index: include/llvm/Support/TarWriter.h
===================================================================
--- include/llvm/Support/TarWriter.h
+++ include/llvm/Support/TarWriter.h
@@ -13,6 +13,7 @@
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/Error.h"
 #include "llvm/Support/raw_ostream.h"
+#include <set>
 
 namespace llvm {
 class TarWriter {
@@ -26,6 +27,7 @@
   TarWriter(int FD, StringRef BaseDir);
   raw_fd_ostream OS;
   std::string BaseDir;
+  std::set<std::string> Files;
 };
 }
 
Index: lib/Support/TarWriter.cpp
===================================================================
--- lib/Support/TarWriter.cpp
+++ lib/Support/TarWriter.cpp
@@ -173,6 +173,10 @@
   // Write Path and Data.
   std::string Fullpath = BaseDir + "/" + sys::path::convert_to_slash(Path);
 
+  // We do not want to include the same file more than once.
+  if (!Files.insert(Fullpath).second)
+    return;
+
   StringRef Prefix;
   StringRef Name;
   if (splitUstar(Fullpath, Prefix, Name)) {