Index: lld/trunk/lib/Core/Reproduce.cpp
===================================================================
--- lld/trunk/lib/Core/Reproduce.cpp
+++ lld/trunk/lib/Core/Reproduce.cpp
@@ -50,6 +50,12 @@
   OS << Data;                            // c_filedata
 }
 
+// Converts path to use unix path separators so the cpio can be extracted on
+// both unix and windows.
+static void convertToUnixPathSeparator(SmallString<128> &Path) {
+  std::replace(Path.begin(), Path.end(), '\\', '/');
+}
+
 void CpioFile::append(StringRef Path, StringRef Data) {
   if (!Seen.insert(Path).second)
     return;
@@ -59,10 +65,7 @@
   // (i.e. in that case we are creating baz.cpio.)
   SmallString<128> Fullpath;
   path::append(Fullpath, Basename, Path);
-
-  // Use unix path separators so the cpio can be extracted on both unix and
-  // windows.
-  std::replace(Fullpath.begin(), Fullpath.end(), '\\', '/');
+  convertToUnixPathSeparator(Fullpath);
 
   writeMember(*OS, Fullpath, Data);
 
@@ -76,6 +79,8 @@
 // Makes a given pathname an absolute path first, and then remove
 // beginning /. For example, "../foo.o" is converted to "home/john/foo.o",
 // assuming that the current directory is "/home/john/bar".
+// Returned string is a backslash-separated path even on Windows to avoid
+// a mess with backslash-as-escape and backslash-as-path-separator.
 std::string lld::relativeToRoot(StringRef Path) {
   SmallString<128> Abs = Path;
   if (sys::fs::make_absolute(Abs))
@@ -93,6 +98,7 @@
     Res = Root.substr(2);
 
   path::append(Res, path::relative_path(Abs));
+  convertToUnixPathSeparator(Res);
 
   return Res.str();
 }
Index: lld/trunk/test/ELF/reproduce-windows2.s
===================================================================
--- lld/trunk/test/ELF/reproduce-windows2.s
+++ lld/trunk/test/ELF/reproduce-windows2.s
@@ -0,0 +1,11 @@
+# REQUIRES: system-windows, x86, cpio
+
+# Test that a response.txt file always uses / instead of \.
+# RUN: rm -rf %t.dir
+# RUN: mkdir -p %t.dir/build
+# RUN: llvm-mc %s -o %t.dir/build/foo.o -filetype=obj -triple=x86_64-pc-linux
+# RUN: cd %t.dir
+# RUN: ld.lld build/foo.o --reproduce repro
+# RUN: echo "*response.txt" > list.txt
+# RUN: cpio -i --to-stdout --pattern-file=list.txt < repro.cpio | FileCheck %s
+# CHECK: {{.*}}/build/foo.o
Index: lld/trunk/test/lit.cfg
===================================================================
--- lld/trunk/test/lit.cfg
+++ lld/trunk/test/lit.cfg
@@ -207,6 +207,10 @@
 if platform.system() in ['FreeBSD', 'Linux']:
     config.available_features.add('system-linker-elf')
 
+# Running on Windows
+if platform.system() in ['Windows']:
+    config.available_features.add('system-windows')
+
 # Set if host-cxxabi's demangler can handle target's symbols.
 if platform.system() not in ['Windows']:
     config.available_features.add('demangler')