Don't warn for unused macro when undef'ing it, if it comes from an included file. rdar://9745065

llvm-svn: 134919

clang/lib/Lex/PPDirectives.cpp

@@ -1594,7 +1594,7 @@ void Preprocessor::HandleUndefDirective(Token &UndefTok) {
   // If the macro is not defined, this is a noop undef, just return.
   if (MI == 0) return;
 
-  if (!MI->isUsed())
+  if (!MI->isUsed() && MI->isWarnIfUnused())
     Diag(MI->getDefinitionLoc(), diag::pp_macro_not_used);
 
   // If the callbacks want to know, tell them about the macro #undef.

clang/test/Preprocessor/warn-macro-unused.c

@@ -1,5 +1,10 @@
 // RUN: %clang_cc1 %s -Wunused-macros -Dfoo -Dfoo -verify
 
+#include "warn-macro-unused.h"
+
 #define unused // expected-warning {{macro is not used}}
 #define unused
 unused
+
+// rdar://9745065
+#undef unused_from_header // no warning