Index: include/llvm/Support/CommandLine.h
===================================================================
--- include/llvm/Support/CommandLine.h
+++ 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: lib/Support/CommandLine.cpp
===================================================================
--- lib/Support/CommandLine.cpp
+++ lib/Support/CommandLine.cpp
@@ -1826,12 +1826,23 @@
 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 (StringMap<cl::Option *>::iterator I = Options.begin(), E = Options.end();
+       I != E; ++I) {
+    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);