Index: llvm/trunk/include/llvm/Support/FileSystem.h
===================================================================
--- llvm/trunk/include/llvm/Support/FileSystem.h
+++ llvm/trunk/include/llvm/Support/FileSystem.h
@@ -357,6 +357,13 @@
 ///          otherwise a platform-specific error_code.
 std::error_code current_path(SmallVectorImpl<char> &result);
 
+/// @brief Set the current path.
+///
+/// @param path The path to set.
+/// @returns errc::success if the current path was successfully set,
+///          otherwise a platform-specific error_code.
+std::error_code set_current_path(const Twine &path);
+
 /// @brief Remove path. Equivalent to POSIX remove().
 ///
 /// @param path Input path.
Index: llvm/trunk/lib/Support/Unix/Path.inc
===================================================================
--- llvm/trunk/lib/Support/Unix/Path.inc
+++ llvm/trunk/lib/Support/Unix/Path.inc
@@ -257,6 +257,16 @@
   return std::error_code();
 }
 
+std::error_code set_current_path(const Twine &path) {
+  SmallString<128> path_storage;
+  StringRef p = path.toNullTerminatedStringRef(path_storage);
+
+  if (::chdir(p.begin()) == -1)
+    return std::error_code(errno, std::generic_category());
+
+  return std::error_code();
+}
+
 std::error_code create_directory(const Twine &path, bool IgnoreExisting,
                                  perms Perms) {
   SmallString<128> path_storage;
Index: llvm/trunk/lib/Support/Windows/Path.inc
===================================================================
--- llvm/trunk/lib/Support/Windows/Path.inc
+++ llvm/trunk/lib/Support/Windows/Path.inc
@@ -200,6 +200,18 @@
   return UTF16ToUTF8(cur_path.begin(), cur_path.size(), result);
 }
 
+std::error_code set_current_path(const Twine &path) {
+  // Convert to utf-16.
+  SmallVector<wchar_t, 128> wide_path;
+  if (std::error_code ec = widenPath(path, wide_path))
+    return ec;
+
+  if (!::SetCurrentDirectoryW(wide_path.begin()))
+    return mapWindowsError(::GetLastError());
+
+  return std::error_code();
+}
+
 std::error_code create_directory(const Twine &path, bool IgnoreExisting,
                                  perms Perms) {
   SmallVector<wchar_t, 128> path_utf16;
Index: llvm/trunk/unittests/Support/Path.cpp
===================================================================
--- llvm/trunk/unittests/Support/Path.cpp
+++ llvm/trunk/unittests/Support/Path.cpp
@@ -1135,4 +1135,23 @@
 
   ::close(FileDescriptor);
 }
+
+TEST_F(FileSystemTest, set_current_path) {
+  SmallString<128> path;
+
+  ASSERT_NO_ERROR(fs::current_path(path));
+  ASSERT_NE(TestDirectory, path);
+
+  struct RestorePath {
+    SmallString<128> path;
+    RestorePath(const SmallString<128> &path) : path(path) {}
+    ~RestorePath() { fs::set_current_path(path); }
+  } restore_path(path);
+
+  ASSERT_NO_ERROR(fs::set_current_path(TestDirectory));
+
+  ASSERT_NO_ERROR(fs::current_path(path));
+  ASSERT_EQ(TestDirectory, path);
+}
+
 } // anonymous namespace