Index: cfe/trunk/include/clang/Basic/DiagnosticGroups.td
===================================================================
--- cfe/trunk/include/clang/Basic/DiagnosticGroups.td
+++ cfe/trunk/include/clang/Basic/DiagnosticGroups.td
@@ -48,6 +48,7 @@
   DiagGroup<"implicit-conversion-floating-point-to-bool">;
 def ObjCLiteralConversion : DiagGroup<"objc-literal-conversion">;
 def BadArrayNewLength : DiagGroup<"bad-array-new-length">;
+def MacroRedefined : DiagGroup<"macro-redefined">;
 def BuiltinMacroRedefined : DiagGroup<"builtin-macro-redefined">;
 def BuiltinRequiresHeader : DiagGroup<"builtin-requires-header">;
 def C99Compat : DiagGroup<"c99-compat">;
Index: cfe/trunk/include/clang/Basic/DiagnosticLexKinds.td
===================================================================
--- cfe/trunk/include/clang/Basic/DiagnosticLexKinds.td
+++ cfe/trunk/include/clang/Basic/DiagnosticLexKinds.td
@@ -316,7 +316,7 @@
 def ext_pp_comma_expr : Extension<"comma operator in operand of #if">;
 def ext_pp_bad_vaargs_use : Extension<
   "__VA_ARGS__ can only appear in the expansion of a C99 variadic macro">;
-def ext_pp_macro_redef : ExtWarn<"%0 macro redefined">;
+def ext_pp_macro_redef : ExtWarn<"%0 macro redefined">, InGroup<MacroRedefined>;
 def ext_variadic_macro : Extension<"variadic macros are a C99 feature">,
   InGroup<VariadicMacros>;
 def warn_cxx98_compat_variadic_macro : Warning<
Index: cfe/trunk/test/Misc/warning-flags.c
===================================================================
--- cfe/trunk/test/Misc/warning-flags.c
+++ cfe/trunk/test/Misc/warning-flags.c
@@ -18,7 +18,7 @@
 
 The list of warnings below should NEVER grow.  It should gradually shrink to 0.
 
-CHECK: Warnings without flags (106):
+CHECK: Warnings without flags (105):
 CHECK-NEXT:   ext_delete_void_ptr_operand
 CHECK-NEXT:   ext_expected_semi_decl_list
 CHECK-NEXT:   ext_explicit_specialization_storage_class
@@ -28,7 +28,6 @@
 CHECK-NEXT:   ext_missing_whitespace_after_macro_name
 CHECK-NEXT:   ext_new_paren_array_nonconst
 CHECK-NEXT:   ext_plain_complex
-CHECK-NEXT:   ext_pp_macro_redef
 CHECK-NEXT:   ext_template_arg_extra_parens
 CHECK-NEXT:   ext_typecheck_comparison_of_pointer_integer
 CHECK-NEXT:   ext_typecheck_cond_incompatible_operands
Index: cfe/trunk/test/Preprocessor/macro_redefined.c
===================================================================
--- cfe/trunk/test/Preprocessor/macro_redefined.c
+++ cfe/trunk/test/Preprocessor/macro_redefined.c
@@ -0,0 +1,19 @@
+// RUN: %clang_cc1 %s -Eonly -verify -Wno-all -Wmacro-redefined -DCLI_MACRO=1 -DWMACRO_REDEFINED
+// RUN: %clang_cc1 %s -Eonly -verify -Wno-all -Wno-macro-redefined -DCLI_MACRO=1
+
+#ifndef WMACRO_REDEFINED
+// expected-no-diagnostics
+#endif
+
+#ifdef WMACRO_REDEFINED
+// expected-note@1 {{previous definition is here}}
+// expected-warning@+2 {{macro redefined}}
+#endif
+#define CLI_MACRO
+
+#ifdef WMACRO_REDEFINED
+// expected-note@+3 {{previous definition is here}}
+// expected-warning@+3 {{macro redefined}}
+#endif
+#define REGULAR_MACRO
+#define REGULAR_MACRO 1