Index: clang-tools-extra/trunk/clang-tidy/tool/clang-tidy-diff.py
===================================================================
--- clang-tools-extra/trunk/clang-tidy/tool/clang-tidy-diff.py
+++ clang-tools-extra/trunk/clang-tidy/tool/clang-tidy-diff.py
@@ -55,6 +55,14 @@
                       help='checks filter, when not specified, use clang-tidy '
                       'default',
                       default='')
+  parser.add_argument('-extra-arg', dest='extra_arg',
+                      action='append', default=[],
+                      help='Additional argument to append to the compiler '
+                      'command line.')
+  parser.add_argument('-extra-arg-before', dest='extra_arg_before',
+                      action='append', default=[],
+                      help='Additional argument to prepend to the compiler '
+                      'command line.')
   clang_tidy_args = []
   argv = sys.argv[1:]
   if '--' in argv:
@@ -113,6 +121,10 @@
   if args.checks != '':
     command.append('-checks=' + quote + args.checks + quote)
   command.extend(lines_by_file.keys())
+  for arg in args.extra_arg:
+      command.append('-extra-arg=%s' % arg)
+  for arg in args.extra_arg_before:
+      command.append('-extra-arg-before=%s' % arg)
   command.extend(clang_tidy_args)
 
   sys.exit(subprocess.call(' '.join(command), shell=True))