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 +55,8 @@
                       help='checks filter, when not specified, use clang-tidy '
                       'default',
                       default='')
+  parser.add_argument('-path', dest='build_path',
+                      help='Path used to read a compile command database.')
   parser.add_argument('-extra-arg', dest='extra_arg',
                       action='append', default=[],
                       help='Additional argument to append to the compiler '
@@ -124,6 +126,8 @@
     command.append('-checks=' + quote + args.checks + quote)
   if args.quiet:
     command.append('-quiet')
+  if args.build_path is not None:
+    command.append('-p=%s' % args.build_path)
   command.extend(lines_by_file.keys())
   for arg in args.extra_arg:
       command.append('-extra-arg=%s' % arg)
Index: clang-tools-extra/trunk/test/clang-tidy/clang-tidy-diff.cpp
===================================================================
--- clang-tools-extra/trunk/test/clang-tidy/clang-tidy-diff.cpp
+++ clang-tools-extra/trunk/test/clang-tidy/clang-tidy-diff.cpp
@@ -2,6 +2,9 @@
 // RUN: clang-tidy -checks=-*,modernize-use-override %t.cpp -- -std=c++11 | FileCheck -check-prefix=CHECK-SANITY %s
 // RUN: not diff -U0 %s %t.cpp | %clang_tidy_diff -checks=-*,modernize-use-override -- -std=c++11 2>&1 | FileCheck %s
 // RUN: not diff -U0 %s %t.cpp | %clang_tidy_diff -checks=-*,modernize-use-override -quiet -- -std=c++11 2>&1 | FileCheck -check-prefix=CHECK-QUIET %s
+// RUN: mkdir -p %T/compilation-database-test/
+// RUN: echo '[{"directory": "%T", "command": "clang++ -o test.o -std=c++11 %t.cpp", "file": "%t.cpp"}]' > %T/compilation-database-test/compile_commands.json
+// RUN: not diff -U0 %s %t.cpp | %clang_tidy_diff -checks=-*,modernize-use-override -path %T/compilation-database-test 2>&1 | FileCheck -check-prefix=CHECK %s
 struct A {
   virtual void f() {}
   virtual void g() {}