diff --git a/llvm/include/llvm/Support/CommandLine.h b/llvm/include/llvm/Support/CommandLine.h
--- a/llvm/include/llvm/Support/CommandLine.h
+++ b/llvm/include/llvm/Support/CommandLine.h
@@ -201,6 +201,8 @@
 
   StringRef getName() const { return Name; }
   StringRef getDescription() const { return Description; }
+
+  SmallPtrSet<Option *, 16> MemberOptions;
 };
 
 // The general Option Category (used as default category).
@@ -283,9 +285,12 @@
   StringRef ArgStr;   // The argument string itself (ex: "help", "o")
   StringRef HelpStr;  // The descriptive text message for -help
   StringRef ValueStr; // String describing what the value of this option is
-  SmallVector<OptionCategory *, 1>
-      Categories;                    // The Categories this option belongs to
-  SmallPtrSet<SubCommand *, 1> Subs; // The subcommands this option belongs to.
+
+  // Return the set of OptionCategories that this Option belongs to.
+  SmallPtrSet<OptionCategory *, 16> getCategories() const;
+
+  // Return the set of SubCommands that this Option belongs to.
+  SmallPtrSet<SubCommand *, 4> getSubCommands() const;
 
   inline enum NumOccurrencesFlag getNumOccurrencesFlag() const {
     return (enum NumOccurrencesFlag)Occurrences;
@@ -317,12 +322,6 @@
     return getNumOccurrencesFlag() == cl::ConsumeAfter;
   }
 
-  bool isInAllSubCommands() const {
-    return any_of(Subs, [](const SubCommand *SC) {
-      return SC == &*AllSubCommands;
-    });
-  }
-
   //-------------------------------------------------------------------------===
   // Accessor functions set by OptionModifiers
   //
@@ -336,16 +335,13 @@
   void setMiscFlag(enum MiscFlags M) { Misc |= M; }
   void setPosition(unsigned pos) { Position = pos; }
   void addCategory(OptionCategory &C);
-  void addSubCommand(SubCommand &S) { Subs.insert(&S); }
 
 protected:
   explicit Option(enum NumOccurrencesFlag OccurrencesFlag,
                   enum OptionHidden Hidden)
       : NumOccurrences(0), Occurrences(OccurrencesFlag), Value(0),
         HiddenFlag(Hidden), Formatting(NormalFormatting), Misc(0),
-        FullyInitialized(false), Position(0), AdditionalVals(0) {
-    Categories.push_back(&GeneralCategory);
-  }
+        FullyInitialized(false), Position(0), AdditionalVals(0) {}
 
   inline void setNumAdditionalVals(unsigned n) { AdditionalVals = n; }
 
@@ -354,7 +350,14 @@
 
   // addArgument - Register this argument with the commandline system.
   //
-  void addArgument();
+  void addArgument(SubCommand &SC);
+
+  // addArgument - Only called in done() method to add default
+  // TopLevelSubCommand.
+  void addArgument() {
+    if (!FullyInitialized)
+      addArgument(*TopLevelSubCommand);
+  }
 
   /// Unregisters this option from the CommandLine system.
   ///
@@ -465,7 +468,7 @@
 
   sub(SubCommand &S) : Sub(S) {}
 
-  template <class Opt> void apply(Opt &O) const { O.addSubCommand(Sub); }
+  template <class Opt> void apply(Opt &O) const { O.addArgument(Sub); }
 };
 
 //===----------------------------------------------------------------------===//
@@ -1772,11 +1775,10 @@
       error("cl::alias must have argument name specified!");
     if (!AliasFor)
       error("cl::alias must have an cl::aliasopt(option) specified!");
-    if (!Subs.empty())
-      error("cl::alias must not have cl::sub(), aliased option's cl::sub() will be used!");
-    Subs = AliasFor->Subs;
-    Categories = AliasFor->Categories;
-    addArgument();
+    for(OptionCategory *Cat: AliasFor->getCategories())
+      addCategory(*Cat);
+    for(SubCommand *SC: AliasFor->getSubCommands())
+      addArgument(*SC);
   }
 
 public:
diff --git a/llvm/lib/Support/CommandLine.cpp b/llvm/lib/Support/CommandLine.cpp
--- a/llvm/lib/Support/CommandLine.cpp
+++ b/llvm/lib/Support/CommandLine.cpp
@@ -142,7 +142,7 @@
   // This collects Options added with the cl::DefaultOption flag. Since they can
   // be overridden, they are not added to the appropriate SubCommands until
   // ParseCommandLineOptions actually runs.
-  SmallVector<Option*, 4> DefaultOptions;
+  SmallVector<std::pair<Option*, SubCommand*>, 4> DefaultOptions;
 
   // This collects the different option categories that have been registered.
   SmallPtrSet<OptionCategory *, 16> RegisteredOptionCategories;
@@ -182,15 +182,16 @@
   }
 
   void addLiteralOption(Option &Opt, StringRef Name) {
-    if (Opt.Subs.empty())
-      addLiteralOption(Opt, &*TopLevelSubCommand, Name);
-    else {
-      for (auto SC : Opt.Subs)
-        addLiteralOption(Opt, SC, Name);
-    }
+    for(SubCommand *SC: Opt.getSubCommands())
+      addLiteralOption(Opt, SC, Name);
   }
 
-  void addOption(Option *O, SubCommand *SC) {
+  void addOption(Option *O, SubCommand *SC, bool ProcessDefaultOptions = false) {
+    if (!ProcessDefaultOptions && O->isDefaultOption()) {
+      DefaultOptions.push_back(std::make_pair(O, SC));
+      return;
+    }
+
     bool HadErrors = false;
     if (O->hasArgStr()) {
       // If it's a DefaultOption, check to make sure it isn't already there.
@@ -232,22 +233,14 @@
       for (const auto &Sub : RegisteredSubCommands) {
         if (SC == Sub)
           continue;
-        addOption(O, Sub);
+        addOption(O, Sub, ProcessDefaultOptions);
       }
     }
   }
 
-  void addOption(Option *O, bool ProcessDefaultOption = false) {
-    if (!ProcessDefaultOption && O->isDefaultOption()) {
-      DefaultOptions.push_back(O);
-      return;
-    }
-
-    if (O->Subs.empty()) {
-      addOption(O, &*TopLevelSubCommand);
-    } else {
-      for (auto SC : O->Subs)
-        addOption(O, SC);
+  void addDefaultOptions() {
+    for (std::pair<Option *, SubCommand *> &DO : DefaultOptions) {
+      addOption(DO.first, DO.second, true);
     }
   }
 
@@ -285,17 +278,8 @@
   }
 
   void removeOption(Option *O) {
-    if (O->Subs.empty())
-      removeOption(O, &*TopLevelSubCommand);
-    else {
-      if (O->isInAllSubCommands()) {
-        for (auto SC : RegisteredSubCommands)
-          removeOption(O, SC);
-      } else {
-        for (auto SC : O->Subs)
-          removeOption(O, SC);
-      }
-    }
+    for (auto SC : RegisteredSubCommands)
+      removeOption(O, SC);
   }
 
   bool hasOptions(const SubCommand &Sub) const {
@@ -324,17 +308,8 @@
   }
 
   void updateArgStr(Option *O, StringRef NewName) {
-    if (O->Subs.empty())
-      updateArgStr(O, NewName, &*TopLevelSubCommand);
-    else {
-      if (O->isInAllSubCommands()) {
-        for (auto SC : RegisteredSubCommands)
-          updateArgStr(O, NewName, SC);
-      } else {
-        for (auto SC : O->Subs)
-          updateArgStr(O, NewName, SC);
-      }
-    }
+    for (auto SC : RegisteredSubCommands)
+      updateArgStr(O, NewName, SC);
   }
 
   void printOptionValues();
@@ -427,13 +402,37 @@
   GlobalParser->MoreHelp.push_back(Help);
 }
 
-void Option::addArgument() {
-  GlobalParser->addOption(this);
+void Option::addArgument(SubCommand &SC) {
+  GlobalParser->addOption(this, &SC);
   FullyInitialized = true;
 }
 
 void Option::removeArgument() { GlobalParser->removeOption(this); }
 
+SmallPtrSet<OptionCategory *, 16> Option::getCategories() const {
+  SmallPtrSet<OptionCategory *, 16> Cats;
+  for (OptionCategory *C: GlobalParser->RegisteredOptionCategories) {
+    if (C->MemberOptions.find(this) != C->MemberOptions.end())
+      Cats.insert(C);
+  }
+  if (Cats.empty())
+    Cats.insert(&GeneralCategory);
+  return Cats;
+}
+
+SmallPtrSet<SubCommand *, 4> Option::getSubCommands() const {
+  // This can happen for enums and literal options.
+  if (ArgStr.empty())
+    return SmallPtrSet<SubCommand *, 4>{&*TopLevelSubCommand};
+
+  SmallPtrSet<SubCommand *, 4> Subs;
+  for (SubCommand *SC : GlobalParser->getRegisteredSubcommands()) {
+    if (SC->OptionsMap.find(ArgStr) != SC->OptionsMap.end())
+      Subs.insert(SC);
+  }
+  return Subs;
+}
+
 void Option::setArgStr(StringRef S) {
   if (FullyInitialized)
     GlobalParser->updateArgStr(this, S);
@@ -444,14 +443,7 @@
 }
 
 void Option::addCategory(OptionCategory &C) {
-  assert(!Categories.empty() && "Categories cannot be empty.");
-  // Maintain backward compatibility by replacing the default GeneralCategory
-  // if it's still set.  Otherwise, just add the new one.  The GeneralCategory
-  // must be explicitly added if you want multiple categories that include it.
-  if (&C != &GeneralCategory && Categories[0] == &GeneralCategory)
-    Categories[0] = &C;
-  else if (find(Categories, &C) == Categories.end())
-    Categories.push_back(&C);
+  C.MemberOptions.insert(this);
 }
 
 void Option::reset() {
@@ -1261,9 +1253,7 @@
   auto &SinkOpts = ChosenSubCommand->SinkOpts;
   auto &OptionsMap = ChosenSubCommand->OptionsMap;
 
-  for (auto O: DefaultOptions) {
-    addOption(O, true);
-  }
+  addDefaultOptions();
 
   if (ConsumeAfterOpt) {
     assert(PositionalOpts.size() > 0 &&
@@ -2163,7 +2153,7 @@
     // options within categories will also be alphabetically sorted.
     for (size_t I = 0, E = Opts.size(); I != E; ++I) {
       Option *Opt = Opts[I].second;
-      for (auto &Cat : Opt->Categories) {
+      for (auto *Cat : Opt->getCategories()) {
         assert(CategorizedOptions.count(Cat) > 0 &&
                "Option has an unregistered category");
         CategorizedOptions[Cat].push_back(Opt);
@@ -2424,7 +2414,7 @@
 
 void cl::HideUnrelatedOptions(cl::OptionCategory &Category, SubCommand &Sub) {
   for (auto &I : Sub.OptionsMap) {
-    for (auto &Cat : I.second->Categories) {
+    for (OptionCategory *Cat : I.second->getCategories()) {
       if (Cat != &Category &&
           Cat != &GenericCategory)
         I.second->setHiddenFlag(cl::ReallyHidden);
@@ -2435,7 +2425,7 @@
 void cl::HideUnrelatedOptions(ArrayRef<const cl::OptionCategory *> Categories,
                               SubCommand &Sub) {
   for (auto &I : Sub.OptionsMap) {
-    for (auto &Cat : I.second->Categories) {
+    for (OptionCategory *Cat : I.second->getCategories()) {
       if (find(Categories, Cat) == Categories.end() && Cat != &GenericCategory)
         I.second->setHiddenFlag(cl::ReallyHidden);
     }
diff --git a/llvm/unittests/Support/CommandLineTest.cpp b/llvm/unittests/Support/CommandLineTest.cpp
--- a/llvm/unittests/Support/CommandLineTest.cpp
+++ b/llvm/unittests/Support/CommandLineTest.cpp
@@ -95,16 +95,16 @@
   cl::Option *Retrieved = Map["test-option"];
   ASSERT_EQ(&TestOption, Retrieved) << "Retrieved wrong option.";
 
-  ASSERT_NE(Retrieved->Categories.end(),
-            find_if(Retrieved->Categories,
+  ASSERT_NE(Retrieved->getCategories().end(),
+            find_if(Retrieved->getCategories(),
                     [&](const llvm::cl::OptionCategory *Cat) {
                       return Cat == &cl::GeneralCategory;
                     }))
       << "Incorrect default option category.";
 
   Retrieved->addCategory(TestCategory);
-  ASSERT_NE(Retrieved->Categories.end(),
-            find_if(Retrieved->Categories,
+  ASSERT_NE(Retrieved->getCategories().end(),
+            find_if(Retrieved->getCategories(),
                     [&](const llvm::cl::OptionCategory *Cat) {
                       return Cat == &TestCategory;
                     }))
@@ -160,8 +160,8 @@
 TEST(CommandLineTest, UseOptionCategory) {
   StackOption<int> TestOption2("test-option", cl::cat(TestCategory));
 
-  ASSERT_NE(TestOption2.Categories.end(),
-            find_if(TestOption2.Categories,
+  ASSERT_NE(TestOption2.getCategories().end(),
+            find_if(TestOption2.getCategories(),
                          [&](const llvm::cl::OptionCategory *Cat) {
                            return Cat == &TestCategory;
                          }))
@@ -172,18 +172,19 @@
   StackOption<int> TestOption2("test-option2", cl::cat(TestCategory),
                                cl::cat(cl::GeneralCategory),
                                cl::cat(cl::GeneralCategory));
+  auto TestOption2Categories = TestOption2.getCategories();
 
   // Make sure cl::GeneralCategory wasn't added twice.
-  ASSERT_EQ(TestOption2.Categories.size(), 2U);
+  ASSERT_EQ(TestOption2Categories.size(), 2U);
 
-  ASSERT_NE(TestOption2.Categories.end(),
-            find_if(TestOption2.Categories,
+  ASSERT_NE(TestOption2Categories.end(),
+            find_if(TestOption2Categories,
                          [&](const llvm::cl::OptionCategory *Cat) {
                            return Cat == &TestCategory;
                          }))
       << "Failed to assign Option Category.";
-  ASSERT_NE(TestOption2.Categories.end(),
-            find_if(TestOption2.Categories,
+  ASSERT_NE(TestOption2Categories.end(),
+            find_if(TestOption2Categories,
                          [&](const llvm::cl::OptionCategory *Cat) {
                            return Cat == &cl::GeneralCategory;
                          }))
@@ -192,20 +193,21 @@
   cl::OptionCategory AnotherCategory("Additional test Options", "Description");
   StackOption<int> TestOption("test-option", cl::cat(TestCategory),
                               cl::cat(AnotherCategory));
-  ASSERT_EQ(TestOption.Categories.end(),
-            find_if(TestOption.Categories,
+  auto TestOptionCategories = TestOption.getCategories();
+  ASSERT_EQ(TestOptionCategories.end(),
+            find_if(TestOptionCategories,
                          [&](const llvm::cl::OptionCategory *Cat) {
                            return Cat == &cl::GeneralCategory;
                          }))
       << "Failed to remove General Category.";
-  ASSERT_NE(TestOption.Categories.end(),
-            find_if(TestOption.Categories,
+  ASSERT_NE(TestOptionCategories.end(),
+            find_if(TestOptionCategories,
                          [&](const llvm::cl::OptionCategory *Cat) {
                            return Cat == &TestCategory;
                          }))
       << "Failed to assign Option Category.";
-  ASSERT_NE(TestOption.Categories.end(),
-            find_if(TestOption.Categories,
+  ASSERT_NE(TestOptionCategories.end(),
+            find_if(TestOptionCategories,
                          [&](const llvm::cl::OptionCategory *Cat) {
                            return Cat == &AnotherCategory;
                          }))