Index: llvm/trunk/include/llvm/Support/CommandLine.h
===================================================================
--- llvm/trunk/include/llvm/Support/CommandLine.h
+++ llvm/trunk/include/llvm/Support/CommandLine.h
@@ -1889,6 +1889,15 @@
                          SmallVectorImpl<const char *> &Argv,
                          bool MarkEOLs = false);
 
+/// \brief Mark all options not part of this category as cl::ReallyHidden.
+///
+/// \param Category the category of options to keep displaying
+///
+/// Some tools (like clang-format) like to be able to hide all options that are
+/// not specific to the tool. This function allows a tool to specify a single
+/// option category to display in the -help output.
+void HideUnrelatedOptions(cl::OptionCategory &Category);
+
 } // End namespace cl
 
 } // End namespace llvm
Index: llvm/trunk/lib/Support/CommandLine.cpp
===================================================================
--- llvm/trunk/lib/Support/CommandLine.cpp
+++ llvm/trunk/lib/Support/CommandLine.cpp
@@ -1826,12 +1826,22 @@
 void cl::getRegisteredOptions(StringMap<Option *> &Map) {
   // Get all the options.
   SmallVector<Option *, 4> PositionalOpts; // NOT USED
-  SmallVector<Option *, 4> SinkOpts; // NOT USED
+  SmallVector<Option *, 4> SinkOpts;       // NOT USED
   assert(Map.size() == 0 && "StringMap must be empty");
   GetOptionInfo(PositionalOpts, SinkOpts, Map);
   return;
 }
 
+void cl::HideUnrelatedOptions(cl::OptionCategory &Category) {
+  StringMap<cl::Option *> Options;
+  cl::getRegisteredOptions(Options);
+  for (auto &I : Options) {
+    if (I.second->Category != &Category && I.first() != "help" &&
+        I.first() != "version")
+      I.second->setHiddenFlag(cl::ReallyHidden);
+  }
+}
+
 void LLVMParseCommandLineOptions(int argc, const char *const *argv,
                                  const char *Overview) {
   llvm::cl::ParseCommandLineOptions(argc, argv, Overview);
Index: llvm/trunk/unittests/Support/CommandLineTest.cpp
===================================================================
--- llvm/trunk/unittests/Support/CommandLineTest.cpp
+++ llvm/trunk/unittests/Support/CommandLineTest.cpp
@@ -230,5 +230,16 @@
   testAliasRequired(array_lengthof(opts2), opts2);
 }
 
+TEST(CommandLineTest, HideUnrelatedOptions) {
+  cl::opt<int> TestOption1("test-option-1");
+  cl::opt<int> TestOption2("test-option-2", cl::cat(TestCategory));
+
+  cl::HideUnrelatedOptions(TestCategory);
+
+  ASSERT_EQ(cl::ReallyHidden, TestOption1.getOptionHiddenFlag())
+      << "Failed to hide extra option.";
+  ASSERT_EQ(cl::NotHidden, TestOption2.getOptionHiddenFlag())
+      << "Hid extra option that should be visable.";
+}
 
 }  // anonymous namespace