Index: include/llvm/Support/TarWriter.h
===================================================================
--- include/llvm/Support/TarWriter.h
+++ include/llvm/Support/TarWriter.h
@@ -11,6 +11,7 @@
 #define LLVM_SUPPORT_TAR_WRITER_H
 
 #include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/StringSet.h"
 #include "llvm/Support/Error.h"
 #include "llvm/Support/raw_ostream.h"
 
@@ -26,6 +27,7 @@
   TarWriter(int FD, StringRef BaseDir);
   raw_fd_ostream OS;
   std::string BaseDir;
+  StringSet<> 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)) {
Index: unittests/Support/TarWriterTest.cpp
===================================================================
--- unittests/Support/TarWriterTest.cpp
+++ unittests/Support/TarWriterTest.cpp
@@ -120,4 +120,61 @@
   StringRef Pax = StringRef((char *)(Buf.data() + 512), 512);
   EXPECT_TRUE(Pax.startswith("211 path=/" + std::string(200, 'x')));
 }
+
+TEST_F(TarWriterTest, MultipleFiles) {
+  SmallString<128> Path;
+  std::error_code EC =
+      sys::fs::createTemporaryFile("TarWriterTest", "tar", Path);
+  EXPECT_FALSE((bool)EC);
+
+  size_t SingleFileTarSize;
+  {
+    Expected<std::unique_ptr<TarWriter>> TarOrErr = TarWriter::create(Path, "");
+    EXPECT_TRUE((bool)TarOrErr);
+    std::unique_ptr<TarWriter> Tar = std::move(*TarOrErr);
+    Tar->append("FooPath", "foo");
+    Tar.reset();
+
+    ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
+        MemoryBuffer::getFile(Path);
+    EXPECT_TRUE((bool)MBOrErr);
+    SingleFileTarSize = (*MBOrErr)->getBufferSize();
+  }
+
+  size_t MultipleFilesTarSize;
+  {
+    Expected<std::unique_ptr<TarWriter>> TarOrErr = TarWriter::create(Path, "");
+    EXPECT_TRUE((bool)TarOrErr);
+    std::unique_ptr<TarWriter> Tar = std::move(*TarOrErr);
+    Tar->append("FooPath", "foo");
+    Tar->append("BarPath", "bar");
+    Tar.reset();
+
+    ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
+        MemoryBuffer::getFile(Path);
+    EXPECT_TRUE((bool)MBOrErr);
+    MultipleFilesTarSize = (*MBOrErr)->getBufferSize();
+  }
+
+  size_t SameFilesTarSize;
+  {
+    Expected<std::unique_ptr<TarWriter>> TarOrErr = TarWriter::create(Path, "");
+    EXPECT_TRUE((bool)TarOrErr);
+    std::unique_ptr<TarWriter> Tar = std::move(*TarOrErr);
+    Tar->append("FooPath", "foo");
+    Tar->append("FooPath", "bar");
+    Tar.reset();
+
+    ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
+        MemoryBuffer::getFile(Path);
+    EXPECT_TRUE((bool)MBOrErr);
+    SameFilesTarSize = (*MBOrErr)->getBufferSize();
+  }
+
+  // Each new file triggers increasing of tar file. At the same time tar
+  // file should prevent using the same path for multiple files and hence
+  // should not add them to archive. We check this logic here.
+  EXPECT_TRUE(MultipleFilesTarSize > SingleFileTarSize);
+  EXPECT_TRUE(SameFilesTarSize == SingleFileTarSize);
+}
 }