do not warn about unknown pragmas in modes that do not handle them (pr9537)

And refactor to have just one place in code that sets up the empty
pragma handlers.

llvm-svn: 196372

clang/include/clang/Lex/Preprocessor.h

@@ -643,6 +643,9 @@ public:
     RemovePragmaHandler(StringRef(), Handler);
   }
 
+  /// Install empty handlers for all pragmas (making them ignored).
+  void IgnorePragmas();
+
   /// \brief Add the specified comment handler to the preprocessor.
   void addCommentHandler(CommentHandler *Handler);
 

clang/lib/Frontend/FrontendActions.cpp

@@ -485,7 +485,7 @@ void PreprocessOnlyAction::ExecuteAction() {
   Preprocessor &PP = getCompilerInstance().getPreprocessor();
 
   // Ignore unknown pragmas.
-  PP.AddPragmaHandler(new EmptyPragmaHandler());
+  PP.IgnorePragmas();
 
   Token Tok;
   // Start parsing the specified input file.

clang/lib/Frontend/PrintPreprocessedOutput.cpp

@@ -704,7 +704,7 @@ static int MacroIDCompare(const id_macro_pair *LHS, const id_macro_pair *RHS) {
 
 static void DoPrintMacros(Preprocessor &PP, raw_ostream *OS) {
   // Ignore unknown pragmas.
-  PP.AddPragmaHandler(new EmptyPragmaHandler());
+  PP.IgnorePragmas();
 
   // -dM mode just scans and ignores all tokens in the files, then dumps out
   // the macro table at the end.

clang/lib/Lex/Pragma.cpp

@@ -1401,3 +1401,14 @@ void Preprocessor::RegisterBuiltinPragmas() {
     AddPragmaHandler(new PragmaRegionHandler("endregion"));
   }
 }
+
+/// Ignore all pragmas, useful for modes such as -Eonly which would otherwise
+/// warn about those pragmas being unknown.
+void Preprocessor::IgnorePragmas() {
+  AddPragmaHandler(new EmptyPragmaHandler());
+  // Also ignore all pragmas in all namespaces created
+  // in Preprocessor::RegisterBuiltinPragmas().
+  AddPragmaHandler("GCC", new EmptyPragmaHandler());
+  AddPragmaHandler("clang", new EmptyPragmaHandler());
+  AddPragmaHandler("STDC", new EmptyPragmaHandler());
+}

clang/lib/Rewrite/Frontend/InclusionRewriter.cpp

@@ -518,13 +518,7 @@ void clang::RewriteIncludesInInput(Preprocessor &PP, raw_ostream *OS,
   InclusionRewriter *Rewrite = new InclusionRewriter(PP, *OS,
                                                      Opts.ShowLineMarkers);
   PP.addPPCallbacks(Rewrite);
-  // Ignore all pragmas, otherwise there will be warnings about unknown pragmas
-  // (because there's nothing to handle them).
-  PP.AddPragmaHandler(new EmptyPragmaHandler());
-  // Ignore also all pragma in all namespaces created
-  // in Preprocessor::RegisterBuiltinPragmas().
-  PP.AddPragmaHandler("GCC", new EmptyPragmaHandler());
-  PP.AddPragmaHandler("clang", new EmptyPragmaHandler());
+  PP.IgnorePragmas();
 
   // First let the preprocessor process the entire file and call callbacks.
   // Callbacks will record which #include's were actually performed.