Index: llvm/trunk/include/llvm/Support/CommandLine.h
===================================================================
--- llvm/trunk/include/llvm/Support/CommandLine.h
+++ llvm/trunk/include/llvm/Support/CommandLine.h
@@ -1803,10 +1803,12 @@
 /// \param [in,out] Argv Command line into which to expand response files.
 /// \param [in] MarkEOLs Mark end of lines and the end of the response file
 /// with nullptrs in the Argv vector.
+/// \param [in] RelativeNames true if names of nested response files must be
+/// resolved relative to including file.
 /// \return true if all @files were expanded successfully or there were none.
 bool ExpandResponseFiles(StringSaver &Saver, TokenizerCallback Tokenizer,
                          SmallVectorImpl<const char *> &Argv,
-                         bool MarkEOLs = false);
+                         bool MarkEOLs = false, bool RelativeNames = false);
 
 /// \brief Mark all options not part of this category as cl::ReallyHidden.
 ///
Index: llvm/trunk/lib/Support/CommandLine.cpp
===================================================================
--- llvm/trunk/lib/Support/CommandLine.cpp
+++ llvm/trunk/lib/Support/CommandLine.cpp
@@ -871,10 +871,10 @@
   return (S.size() >= 3 && S[0] == '\xef' && S[1] == '\xbb' && S[2] == '\xbf');
 }
 
-static bool ExpandResponseFile(const char *FName, StringSaver &Saver,
+static bool ExpandResponseFile(StringRef FName, StringSaver &Saver,
                                TokenizerCallback Tokenizer,
                                SmallVectorImpl<const char *> &NewArgv,
-                               bool MarkEOLs = false) {
+                               bool MarkEOLs, bool RelativeNames) {
   ErrorOr<std::unique_ptr<MemoryBuffer>> MemBufOrErr =
       MemoryBuffer::getFile(FName);
   if (!MemBufOrErr)
@@ -899,6 +899,25 @@
   // Tokenize the contents into NewArgv.
   Tokenizer(Str, Saver, NewArgv, MarkEOLs);
 
+  // If names of nested response files should be resolved relative to including
+  // file, replace the included response file names with their full paths
+  // obtained by required resolution.
+  if (RelativeNames)
+    for (unsigned I = 0; I < NewArgv.size(); ++I)
+      if (NewArgv[I]) {
+        StringRef Arg = NewArgv[I];
+        if (Arg.front() == '@') {
+          StringRef FileName = Arg.drop_front();
+          if (llvm::sys::path::is_relative(FileName)) {
+            SmallString<128> ResponseFile;
+            ResponseFile.append(1, '@');
+            llvm::sys::path::append(
+                ResponseFile, llvm::sys::path::parent_path(FName), FileName);
+            NewArgv[I] = Saver.save(ResponseFile.c_str()).data();
+          }
+        }
+      }
+
   return true;
 }
 
@@ -906,7 +925,7 @@
 /// StringSaver and tokenization strategy.
 bool cl::ExpandResponseFiles(StringSaver &Saver, TokenizerCallback Tokenizer,
                              SmallVectorImpl<const char *> &Argv,
-                             bool MarkEOLs) {
+                             bool MarkEOLs, bool RelativeNames) {
   unsigned RspFiles = 0;
   bool AllExpanded = true;
 
@@ -930,11 +949,9 @@
 
     // Replace this response file argument with the tokenization of its
     // contents.  Nested response files are expanded in subsequent iterations.
-    // FIXME: If a nested response file uses a relative path, is it relative to
-    // the cwd of the process or the response file?
     SmallVector<const char *, 0> ExpandedArgv;
     if (!ExpandResponseFile(Arg + 1, Saver, Tokenizer, ExpandedArgv,
-                            MarkEOLs)) {
+                            MarkEOLs, RelativeNames)) {
       // We couldn't read this file, so we leave it in the argument stream and
       // move on.
       AllExpanded = false;
Index: llvm/trunk/unittests/Support/CommandLineTest.cpp
===================================================================
--- llvm/trunk/unittests/Support/CommandLineTest.cpp
+++ llvm/trunk/unittests/Support/CommandLineTest.cpp
@@ -7,11 +7,15 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "llvm/ADT/SmallString.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/Config/config.h"
 #include "llvm/Support/CommandLine.h"
+#include "llvm/Support/FileSystem.h"
+#include "llvm/Support/Path.h"
 #include "llvm/Support/StringSaver.h"
 #include "gtest/gtest.h"
+#include <fstream>
 #include <stdlib.h>
 #include <string>
 
@@ -505,4 +509,65 @@
   }
 }
 
+TEST(CommandLineTest, ResponseFiles) {
+  llvm::SmallString<128> TestDir;
+  std::error_code EC =
+    llvm::sys::fs::createUniqueDirectory("unittest", TestDir);
+  EXPECT_TRUE(!EC);
+
+  // Create included response file of first level.
+  llvm::SmallString<128> IncludedFileName;
+  llvm::sys::path::append(IncludedFileName, TestDir, "resp1");
+  std::ofstream IncludedFile(IncludedFileName.c_str());
+  EXPECT_TRUE(IncludedFile.is_open());
+  IncludedFile << "-option_1 -option_2\n"
+                  "@incdir/resp2\n"
+                  "-option_3=abcd\n";
+  IncludedFile.close();
+
+  // Directory for included file.
+  llvm::SmallString<128> IncDir;
+  llvm::sys::path::append(IncDir, TestDir, "incdir");
+  EC = llvm::sys::fs::create_directory(IncDir);
+  EXPECT_TRUE(!EC);
+
+  // Create included response file of second level.
+  llvm::SmallString<128> IncludedFileName2;
+  llvm::sys::path::append(IncludedFileName2, IncDir, "resp2");
+  std::ofstream IncludedFile2(IncludedFileName2.c_str());
+  EXPECT_TRUE(IncludedFile2.is_open());
+  IncludedFile2 << "-option_21 -option_22\n";
+  IncludedFile2 << "-option_23=abcd\n";
+  IncludedFile2.close();
+
+  // Prepare 'file' with reference to response file.
+  SmallString<128> IncRef;
+  IncRef.append(1, '@');
+  IncRef.append(IncludedFileName.c_str());
+  llvm::SmallVector<const char *, 4> Argv =
+                          { "test/test", "-flag_1", IncRef.c_str(), "-flag_2" };
+
+  // Expand response files.
+  llvm::BumpPtrAllocator A;
+  llvm::StringSaver Saver(A);
+  bool Res = llvm::cl::ExpandResponseFiles(
+                    Saver, llvm::cl::TokenizeGNUCommandLine, Argv, false, true);
+  EXPECT_TRUE(Res);
+  EXPECT_EQ(Argv.size(), 9);
+  EXPECT_STREQ(Argv[0], "test/test");
+  EXPECT_STREQ(Argv[1], "-flag_1");
+  EXPECT_STREQ(Argv[2], "-option_1");
+  EXPECT_STREQ(Argv[3], "-option_2");
+  EXPECT_STREQ(Argv[4], "-option_21");
+  EXPECT_STREQ(Argv[5], "-option_22");
+  EXPECT_STREQ(Argv[6], "-option_23=abcd");
+  EXPECT_STREQ(Argv[7], "-option_3=abcd");
+  EXPECT_STREQ(Argv[8], "-flag_2");
+
+  llvm::sys::fs::remove(IncludedFileName2);
+  llvm::sys::fs::remove(IncDir);
+  llvm::sys::fs::remove(IncludedFileName);
+  llvm::sys::fs::remove(TestDir);
+}
+
 }  // anonymous namespace