Index: llvm/trunk/include/llvm/Support/CommandLine.h
===================================================================
--- llvm/trunk/include/llvm/Support/CommandLine.h
+++ llvm/trunk/include/llvm/Support/CommandLine.h
@@ -21,10 +21,12 @@
 #define LLVM_SUPPORT_COMMANDLINE_H
 
 #include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringMap.h"
 #include "llvm/ADT/Twine.h"
 #include "llvm/Support/Compiler.h"
+#include "llvm/Support/ManagedStatic.h"
 #include <cassert>
 #include <climits>
 #include <cstdarg>
@@ -43,8 +45,9 @@
 //===----------------------------------------------------------------------===//
 // ParseCommandLineOptions - Command line option processing entry point.
 //
-void ParseCommandLineOptions(int argc, const char *const *argv,
-                             const char *Overview = nullptr);
+bool ParseCommandLineOptions(int argc, const char *const *argv,
+                             const char *Overview = nullptr,
+                             bool IgnoreErrors = false);
 
 //===----------------------------------------------------------------------===//
 // ParseEnvironmentOptions - Environment variable option processing alternate
@@ -171,6 +174,45 @@
 extern OptionCategory GeneralCategory;
 
 //===----------------------------------------------------------------------===//
+// SubCommand class
+//
+class SubCommand {
+private:
+  const char *const Name = nullptr;
+  const char *const Description = nullptr;
+
+protected:
+  void registerSubCommand();
+  void unregisterSubCommand();
+
+public:
+  SubCommand(const char *const Name, const char *const Description = nullptr)
+      : Name(Name), Description(Description) {
+    registerSubCommand();
+  }
+  SubCommand() {}
+
+  void reset();
+
+  operator bool() const;
+
+  const char *getName() const { return Name; }
+  const char *getDescription() const { return Description; }
+
+  SmallVector<Option *, 4> PositionalOpts;
+  SmallVector<Option *, 4> SinkOpts;
+  StringMap<Option *> OptionsMap;
+
+  Option *ConsumeAfterOpt = nullptr; // The ConsumeAfter option if it exists.
+};
+
+// A special subcommand representing no subcommand
+extern ManagedStatic<SubCommand> TopLevelSubCommand;
+
+// A special subcommand that can be used to put an option into all subcommands.
+extern ManagedStatic<SubCommand> AllSubCommands;
+
+//===----------------------------------------------------------------------===//
 // Option Base class
 //
 class alias;
@@ -209,6 +251,7 @@
   StringRef HelpStr;  // The descriptive text message for -help
   StringRef ValueStr; // String describing what the value of this option is
   OptionCategory *Category; // The Category this option belongs to
+  SmallPtrSet<SubCommand *, 4> Subs; // The subcommands this option belongs to.
   bool FullyInitialized;    // Has addArguemnt been called?
 
   inline enum NumOccurrencesFlag getNumOccurrencesFlag() const {
@@ -229,6 +272,16 @@
 
   // hasArgStr - Return true if the argstr != ""
   bool hasArgStr() const { return !ArgStr.empty(); }
+  bool isPositional() const { return getFormattingFlag() == cl::Positional; }
+  bool isSink() const { return getMiscFlags() & cl::Sink; }
+  bool isConsumeAfter() const {
+    return getNumOccurrencesFlag() == cl::ConsumeAfter;
+  }
+  bool isInAllSubCommands() const {
+    return std::any_of(Subs.begin(), Subs.end(), [](const SubCommand *SC) {
+      return SC == &*AllSubCommands;
+    });
+  }
 
   //-------------------------------------------------------------------------===
   // Accessor functions set by OptionModifiers
@@ -243,6 +296,7 @@
   void setMiscFlag(enum MiscFlags M) { Misc |= M; }
   void setPosition(unsigned pos) { Position = pos; }
   void setCategory(OptionCategory &C) { Category = &C; }
+  void addSubCommand(SubCommand &S) { Subs.insert(&S); }
 
 protected:
   explicit Option(enum NumOccurrencesFlag OccurrencesFlag,
@@ -287,6 +341,7 @@
 
 public:
   inline int getNumOccurrences() const { return NumOccurrences; }
+  inline void reset() { NumOccurrences = 0; }
   virtual ~Option() {}
 };
 
@@ -349,6 +404,14 @@
   template <class Opt> void apply(Opt &O) const { O.setCategory(Category); }
 };
 
+// sub - Specify the subcommand that this option belongs to.
+struct sub {
+  SubCommand &Sub;
+  sub(SubCommand &S) : Sub(S) {}
+
+  template <class Opt> void apply(Opt &O) const { O.addSubCommand(Sub); }
+};
+
 //===----------------------------------------------------------------------===//
 // OptionValue class
 
@@ -1589,6 +1652,7 @@
       error("cl::alias must have argument name specified!");
     if (!AliasFor)
       error("cl::alias must have an cl::aliasopt(option) specified!");
+    Subs = AliasFor->Subs;
     addArgument();
   }
 
@@ -1669,7 +1733,7 @@
 /// Hopefully this API can be depricated soon. Any situation where options need
 /// to be modified by tools or libraries should be handled by sane APIs rather
 /// than just handing around a global list.
-StringMap<Option *> &getRegisteredOptions();
+StringMap<Option *> &getRegisteredOptions(SubCommand &Sub);
 
 //===----------------------------------------------------------------------===//
 // Standalone command line processing utilities.
@@ -1737,7 +1801,8 @@
 /// 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);
+void HideUnrelatedOptions(cl::OptionCategory &Category,
+                          SubCommand &Sub = *TopLevelSubCommand);
 
 /// \brief Mark all options not part of the categories as cl::ReallyHidden.
 ///
@@ -1746,7 +1811,10 @@
 /// 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(ArrayRef<const cl::OptionCategory *> Categories);
+void HideUnrelatedOptions(ArrayRef<const cl::OptionCategory *> Categories,
+                          SubCommand &Sub = *TopLevelSubCommand);
+
+void ResetCommandLineOptions();
 
 } // End namespace cl
 
Index: llvm/trunk/lib/Support/CommandLine.cpp
===================================================================
--- llvm/trunk/lib/Support/CommandLine.cpp
+++ llvm/trunk/lib/Support/CommandLine.cpp
@@ -19,6 +19,7 @@
 #include "llvm/Support/CommandLine.h"
 #include "llvm-c/Support.h"
 #include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/SmallString.h"
@@ -94,35 +95,54 @@
   // This collects additional help to be printed.
   std::vector<const char *> MoreHelp;
 
-  SmallVector<Option *, 4> PositionalOpts;
-  SmallVector<Option *, 4> SinkOpts;
-  StringMap<Option *> OptionsMap;
-
-  Option *ConsumeAfterOpt; // The ConsumeAfter option if it exists.
-
   // This collects the different option categories that have been registered.
   SmallPtrSet<OptionCategory *, 16> RegisteredOptionCategories;
 
-  CommandLineParser() : ProgramOverview(nullptr), ConsumeAfterOpt(nullptr) {}
+  // This collects the different subcommands that have been registered.
+  SmallPtrSet<SubCommand *, 4> RegisteredSubCommands;
 
-  void ParseCommandLineOptions(int argc, const char *const *argv,
-                               const char *Overview);
+  CommandLineParser() : ProgramOverview(nullptr), ActiveSubCommand(nullptr) {
+    registerSubCommand(&*TopLevelSubCommand);
+    registerSubCommand(&*AllSubCommands);
+  }
 
-  void addLiteralOption(Option &Opt, const char *Name) {
-    if (!Opt.hasArgStr()) {
-      if (!OptionsMap.insert(std::make_pair(Name, &Opt)).second) {
-        errs() << ProgramName << ": CommandLine Error: Option '" << Name
-               << "' registered more than once!\n";
-        report_fatal_error("inconsistency in registered CommandLine options");
+  bool ParseCommandLineOptions(int argc, const char *const *argv,
+                               const char *Overview, bool IgnoreErrors);
+
+  void addLiteralOption(Option &Opt, SubCommand *SC, const char *Name) {
+    if (Opt.hasArgStr())
+      return;
+    if (!SC->OptionsMap.insert(std::make_pair(Name, &Opt)).second) {
+      errs() << ProgramName << ": CommandLine Error: Option '" << Name
+             << "' registered more than once!\n";
+      report_fatal_error("inconsistency in registered CommandLine options");
+    }
+
+    // If we're adding this to all sub-commands, add it to the ones that have
+    // already been registered.
+    if (SC == &*AllSubCommands) {
+      for (const auto &Sub : RegisteredSubCommands) {
+        if (SC == Sub)
+          continue;
+        addLiteralOption(Opt, Sub, Name);
       }
     }
   }
 
-  void addOption(Option *O) {
+  void addLiteralOption(Option &Opt, const char *Name) {
+    if (Opt.Subs.empty())
+      addLiteralOption(Opt, &*TopLevelSubCommand, Name);
+    else {
+      for (auto SC : Opt.Subs)
+        addLiteralOption(Opt, SC, Name);
+    }
+  }
+
+  void addOption(Option *O, SubCommand *SC) {
     bool HadErrors = false;
     if (O->hasArgStr()) {
       // Add argument to the argument map!
-      if (!OptionsMap.insert(std::make_pair(O->ArgStr, O)).second) {
+      if (!SC->OptionsMap.insert(std::make_pair(O->ArgStr, O)).second) {
         errs() << ProgramName << ": CommandLine Error: Option '" << O->ArgStr
                << "' registered more than once!\n";
         HadErrors = true;
@@ -131,15 +151,15 @@
 
     // Remember information about positional options.
     if (O->getFormattingFlag() == cl::Positional)
-      PositionalOpts.push_back(O);
+      SC->PositionalOpts.push_back(O);
     else if (O->getMiscFlags() & cl::Sink) // Remember sink options
-      SinkOpts.push_back(O);
+      SC->SinkOpts.push_back(O);
     else if (O->getNumOccurrencesFlag() == cl::ConsumeAfter) {
-      if (ConsumeAfterOpt) {
+      if (SC->ConsumeAfterOpt) {
         O->error("Cannot specify more than one option with cl::ConsumeAfter!");
         HadErrors = true;
       }
-      ConsumeAfterOpt = O;
+      SC->ConsumeAfterOpt = O;
     }
 
     // Fail hard if there were errors. These are strictly unrecoverable and
@@ -148,47 +168,102 @@
     // linked LLVM distribution.
     if (HadErrors)
       report_fatal_error("inconsistency in registered CommandLine options");
+
+    // If we're adding this to all sub-commands, add it to the ones that have
+    // already been registered.
+    if (SC == &*AllSubCommands) {
+      for (const auto &Sub : RegisteredSubCommands) {
+        if (SC == Sub)
+          continue;
+        addOption(O, Sub);
+      }
+    }
   }
 
-  void removeOption(Option *O) {
+  void addOption(Option *O) {
+    if (O->Subs.empty()) {
+      addOption(O, &*TopLevelSubCommand);
+    } else {
+      for (auto SC : O->Subs)
+        addOption(O, SC);
+    }
+  }
+
+  void removeOption(Option *O, SubCommand *SC) {
     SmallVector<StringRef, 16> OptionNames;
     O->getExtraOptionNames(OptionNames);
     if (O->hasArgStr())
       OptionNames.push_back(O->ArgStr);
+
+    SubCommand &Sub = *SC;
     for (auto Name : OptionNames)
-      OptionsMap.erase(Name);
+      Sub.OptionsMap.erase(Name);
 
     if (O->getFormattingFlag() == cl::Positional)
-      for (auto Opt = PositionalOpts.begin(); Opt != PositionalOpts.end();
-           ++Opt) {
+      for (auto Opt = Sub.PositionalOpts.begin();
+           Opt != Sub.PositionalOpts.end(); ++Opt) {
         if (*Opt == O) {
-          PositionalOpts.erase(Opt);
+          Sub.PositionalOpts.erase(Opt);
           break;
         }
       }
     else if (O->getMiscFlags() & cl::Sink)
-      for (auto Opt = SinkOpts.begin(); Opt != SinkOpts.end(); ++Opt) {
+      for (auto Opt = Sub.SinkOpts.begin(); Opt != Sub.SinkOpts.end(); ++Opt) {
         if (*Opt == O) {
-          SinkOpts.erase(Opt);
+          Sub.SinkOpts.erase(Opt);
           break;
         }
       }
-    else if (O == ConsumeAfterOpt)
-      ConsumeAfterOpt = nullptr;
+    else if (O == Sub.ConsumeAfterOpt)
+      Sub.ConsumeAfterOpt = nullptr;
   }
 
-  bool hasOptions() {
-    return (!OptionsMap.empty() || !PositionalOpts.empty() ||
-            nullptr != ConsumeAfterOpt);
+  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);
+      }
+    }
   }
 
-  void updateArgStr(Option *O, StringRef NewName) {
-    if (!OptionsMap.insert(std::make_pair(NewName, O)).second) {
+  bool hasOptions(const SubCommand &Sub) const {
+    return (!Sub.OptionsMap.empty() || !Sub.PositionalOpts.empty() ||
+            nullptr != Sub.ConsumeAfterOpt);
+  }
+
+  bool hasOptions() const {
+    for (const auto &S : RegisteredSubCommands) {
+      if (hasOptions(*S))
+        return true;
+    }
+    return false;
+  }
+
+  SubCommand *getActiveSubCommand() { return ActiveSubCommand; }
+
+  void updateArgStr(Option *O, StringRef NewName, SubCommand *SC) {
+    SubCommand &Sub = *SC;
+    if (!Sub.OptionsMap.insert(std::make_pair(NewName, O)).second) {
       errs() << ProgramName << ": CommandLine Error: Option '" << O->ArgStr
              << "' registered more than once!\n";
       report_fatal_error("inconsistency in registered CommandLine options");
     }
-    OptionsMap.erase(O->ArgStr);
+    Sub.OptionsMap.erase(O->ArgStr);
+  }
+
+  void updateArgStr(Option *O, StringRef NewName) {
+    if (O->Subs.empty())
+      updateArgStr(O, NewName, &*TopLevelSubCommand);
+    else {
+      for (auto SC : O->Subs)
+        updateArgStr(O, NewName, SC);
+    }
   }
 
   void printOptionValues();
@@ -203,8 +278,58 @@
     RegisteredOptionCategories.insert(cat);
   }
 
+  void registerSubCommand(SubCommand *sub) {
+    assert(count_if(RegisteredSubCommands,
+                    [sub](const SubCommand *Sub) {
+                      return (sub->getName() != nullptr) &&
+                             (Sub->getName() == sub->getName());
+                    }) == 0 &&
+           "Duplicate subcommands");
+    RegisteredSubCommands.insert(sub);
+
+    // For all options that have been registered for all subcommands, add the
+    // option to this subcommand now.
+    if (sub != &*AllSubCommands) {
+      for (auto &E : AllSubCommands->OptionsMap) {
+        Option *O = E.second;
+        if ((O->isPositional() || O->isSink() || O->isConsumeAfter()) ||
+            O->hasArgStr())
+          addOption(O, sub);
+        else
+          addLiteralOption(*O, sub, E.first().str().c_str());
+      }
+    }
+  }
+
+  void unregisterSubCommand(SubCommand *sub) {
+    RegisteredSubCommands.erase(sub);
+  }
+
+  void reset() {
+    ActiveSubCommand = nullptr;
+    ProgramName.clear();
+    ProgramOverview = nullptr;
+
+    MoreHelp.clear();
+    RegisteredOptionCategories.clear();
+
+    for (auto SC : RegisteredSubCommands) {
+      for (auto &O : SC->OptionsMap)
+        O.second->reset();
+    }
+    RegisteredSubCommands.clear();
+
+    TopLevelSubCommand->reset();
+    AllSubCommands->reset();
+    registerSubCommand(&*TopLevelSubCommand);
+    registerSubCommand(&*AllSubCommands);
+  }
+
 private:
-  Option *LookupOption(StringRef &Arg, StringRef &Value);
+  SubCommand *ActiveSubCommand;
+
+  Option *LookupOption(SubCommand &Sub, StringRef &Arg, StringRef &Value);
+  SubCommand *LookupSubCommand(const char *Name);
 };
 
 } // namespace
@@ -239,6 +364,32 @@
   GlobalParser->registerCategory(this);
 }
 
+// A special subcommand representing no subcommand
+ManagedStatic<SubCommand> llvm::cl::TopLevelSubCommand;
+
+// A special subcommand that can be used to put an option into all subcommands.
+ManagedStatic<SubCommand> llvm::cl::AllSubCommands;
+
+void SubCommand::registerSubCommand() {
+  GlobalParser->registerSubCommand(this);
+}
+
+void SubCommand::unregisterSubCommand() {
+  GlobalParser->unregisterSubCommand(this);
+}
+
+void SubCommand::reset() {
+  PositionalOpts.clear();
+  SinkOpts.clear();
+  OptionsMap.clear();
+
+  ConsumeAfterOpt = nullptr;
+}
+
+SubCommand::operator bool() const {
+  return (GlobalParser->getActiveSubCommand() == this);
+}
+
 //===----------------------------------------------------------------------===//
 // Basic, shared command line option processing machinery.
 //
@@ -246,25 +397,29 @@
 /// LookupOption - Lookup the option specified by the specified option on the
 /// command line.  If there is a value specified (after an equal sign) return
 /// that as well.  This assumes that leading dashes have already been stripped.
-Option *CommandLineParser::LookupOption(StringRef &Arg, StringRef &Value) {
+Option *CommandLineParser::LookupOption(SubCommand &Sub, StringRef &Arg,
+                                        StringRef &Value) {
   // Reject all dashes.
   if (Arg.empty())
     return nullptr;
+  assert(&Sub != &*AllSubCommands);
 
   size_t EqualPos = Arg.find('=');
 
   // If we have an equals sign, remember the value.
   if (EqualPos == StringRef::npos) {
     // Look up the option.
-    StringMap<Option *>::const_iterator I = OptionsMap.find(Arg);
-    return I != OptionsMap.end() ? I->second : nullptr;
+    auto I = Sub.OptionsMap.find(Arg);
+    if (I == Sub.OptionsMap.end())
+      return nullptr;
+
+    return I != Sub.OptionsMap.end() ? I->second : nullptr;
   }
 
   // If the argument before the = is a valid option name, we match.  If not,
   // return Arg unmolested.
-  StringMap<Option *>::const_iterator I =
-      OptionsMap.find(Arg.substr(0, EqualPos));
-  if (I == OptionsMap.end())
+  auto I = Sub.OptionsMap.find(Arg.substr(0, EqualPos));
+  if (I == Sub.OptionsMap.end())
     return nullptr;
 
   Value = Arg.substr(EqualPos + 1);
@@ -272,6 +427,21 @@
   return I->second;
 }
 
+SubCommand *CommandLineParser::LookupSubCommand(const char *Name) {
+  if (Name == nullptr)
+    return &*TopLevelSubCommand;
+  for (auto S : RegisteredSubCommands) {
+    if (S == &*AllSubCommands)
+      continue;
+    if (S->getName() == nullptr)
+      continue;
+
+    if (StringRef(S->getName()) == StringRef(Name))
+      return S;
+  }
+  return &*TopLevelSubCommand;
+}
+
 /// LookupNearestOption - Lookup the closest match to the option specified by
 /// the specified option on the command line.  If there is a value specified
 /// (after an equal sign) return that as well.  This assumes that leading dashes
@@ -820,14 +990,16 @@
   ParseCommandLineOptions(newArgc, &newArgv[0], Overview);
 }
 
-void cl::ParseCommandLineOptions(int argc, const char *const *argv,
-                                 const char *Overview) {
-  GlobalParser->ParseCommandLineOptions(argc, argv, Overview);
+bool cl::ParseCommandLineOptions(int argc, const char *const *argv,
+                                 const char *Overview, bool IgnoreErrors) {
+  return GlobalParser->ParseCommandLineOptions(argc, argv, Overview,
+                                               IgnoreErrors);
 }
 
-void CommandLineParser::ParseCommandLineOptions(int argc,
+bool CommandLineParser::ParseCommandLineOptions(int argc,
                                                 const char *const *argv,
-                                                const char *Overview) {
+                                                const char *Overview,
+                                                bool IgnoreErrors) {
   assert(hasOptions() && "No options specified!");
 
   // Expand response files.
@@ -850,6 +1022,30 @@
   // Determine whether or not there are an unlimited number of positionals
   bool HasUnlimitedPositionals = false;
 
+  // So that we can parse different command lines multiple times in succession
+  // we reset all option values to look like they have never been seen before.
+  for (auto SC : RegisteredSubCommands) {
+    for (auto &O : SC->OptionsMap)
+      O.second->reset();
+  }
+
+  int FirstArg = 1;
+  SubCommand *ChosenSubCommand = &*TopLevelSubCommand;
+  if (argc >= 2 && argv[FirstArg][0] != '-') {
+    // If the first argument specifies a valid subcommand, start processing
+    // options from the second argument.
+    ChosenSubCommand = LookupSubCommand(argv[FirstArg]);
+    if (ChosenSubCommand != &*TopLevelSubCommand)
+      FirstArg = 2;
+  }
+  GlobalParser->ActiveSubCommand = ChosenSubCommand;
+
+  assert(ChosenSubCommand);
+  auto &ConsumeAfterOpt = ChosenSubCommand->ConsumeAfterOpt;
+  auto &PositionalOpts = ChosenSubCommand->PositionalOpts;
+  auto &SinkOpts = ChosenSubCommand->SinkOpts;
+  auto &OptionsMap = ChosenSubCommand->OptionsMap;
+
   if (ConsumeAfterOpt) {
     assert(PositionalOpts.size() > 0 &&
            "Cannot specify cl::ConsumeAfter without a positional argument!");
@@ -865,23 +1061,28 @@
       else if (ConsumeAfterOpt) {
         // ConsumeAfter cannot be combined with "optional" positional options
         // unless there is only one positional argument...
-        if (PositionalOpts.size() > 1)
-          ErrorParsing |= Opt->error(
-              "error - this positional option will never be matched, "
-              "because it does not Require a value, and a "
-              "cl::ConsumeAfter option is active!");
+        if (PositionalOpts.size() > 1) {
+          if (!IgnoreErrors)
+            Opt->error("error - this positional option will never be matched, "
+                       "because it does not Require a value, and a "
+                       "cl::ConsumeAfter option is active!");
+          ErrorParsing = true;
+        }
       } else if (UnboundedFound && !Opt->hasArgStr()) {
         // This option does not "require" a value...  Make sure this option is
         // not specified after an option that eats all extra arguments, or this
         // one will never get any!
         //
-        ErrorParsing |= Opt->error("error - option can never match, because "
-                                   "another positional argument will match an "
-                                   "unbounded number of values, and this option"
-                                   " does not require a value!");
-        errs() << ProgramName << ": CommandLine Error: Option '" << Opt->ArgStr
-               << "' is all messed up!\n";
-        errs() << PositionalOpts.size();
+        if (!IgnoreErrors) {
+          Opt->error("error - option can never match, because "
+                     "another positional argument will match an "
+                     "unbounded number of values, and this option"
+                     " does not require a value!");
+          errs() << ProgramName << ": CommandLine Error: Option '"
+                 << Opt->ArgStr << "' is all messed up!\n";
+          errs() << PositionalOpts.size();
+        }
+        ErrorParsing = true;
       }
       UnboundedFound |= EatsUnboundedNumberOfValues(Opt);
     }
@@ -900,7 +1101,7 @@
 
   // Loop over all of the arguments... processing them.
   bool DashDashFound = false; // Have we read '--'?
-  for (int i = 1; i < argc; ++i) {
+  for (int i = FirstArg; i < argc; ++i) {
     Option *Handler = nullptr;
     Option *NearestHandler = nullptr;
     std::string NearestHandlerString;
@@ -947,7 +1148,7 @@
       while (!ArgName.empty() && ArgName[0] == '-')
         ArgName = ArgName.substr(1);
 
-      Handler = LookupOption(ArgName, Value);
+      Handler = LookupOption(*ChosenSubCommand, ArgName, Value);
       if (!Handler || Handler->getFormattingFlag() != cl::Positional) {
         ProvidePositionalOption(ActivePositionalArg, argv[i], i);
         continue; // We are done!
@@ -959,7 +1160,7 @@
       while (!ArgName.empty() && ArgName[0] == '-')
         ArgName = ArgName.substr(1);
 
-      Handler = LookupOption(ArgName, Value);
+      Handler = LookupOption(*ChosenSubCommand, ArgName, Value);
 
       // Check to see if this "option" is really a prefixed or grouped argument.
       if (!Handler)
@@ -975,13 +1176,15 @@
 
     if (!Handler) {
       if (SinkOpts.empty()) {
-        errs() << ProgramName << ": Unknown command line argument '" << argv[i]
-               << "'.  Try: '" << argv[0] << " -help'\n";
-
-        if (NearestHandler) {
-          // If we know a near match, report it as well.
-          errs() << ProgramName << ": Did you mean '-" << NearestHandlerString
-                 << "'?\n";
+        if (!IgnoreErrors) {
+          errs() << ProgramName << ": Unknown command line argument '"
+                 << argv[i] << "'.  Try: '" << argv[0] << " -help'\n";
+
+          if (NearestHandler) {
+            // If we know a near match, report it as well.
+            errs() << ProgramName << ": Did you mean '-" << NearestHandlerString
+                   << "'?\n";
+          }
         }
 
         ErrorParsing = true;
@@ -1004,17 +1207,21 @@
 
   // Check and handle positional arguments now...
   if (NumPositionalRequired > PositionalVals.size()) {
-    errs() << ProgramName
-           << ": Not enough positional command line arguments specified!\n"
-           << "Must specify at least " << NumPositionalRequired
-           << " positional arguments: See: " << argv[0] << " -help\n";
+    if (!IgnoreErrors) {
+      errs() << ProgramName
+             << ": Not enough positional command line arguments specified!\n"
+             << "Must specify at least " << NumPositionalRequired
+             << " positional arguments: See: " << argv[0] << " -help\n";
+    }
 
     ErrorParsing = true;
   } else if (!HasUnlimitedPositionals &&
              PositionalVals.size() > PositionalOpts.size()) {
-    errs() << ProgramName << ": Too many positional arguments specified!\n"
-           << "Can specify at most " << PositionalOpts.size()
-           << " positional arguments: See: " << argv[0] << " -help\n";
+    if (!IgnoreErrors) {
+      errs() << ProgramName << ": Too many positional arguments specified!\n"
+             << "Can specify at most " << PositionalOpts.size()
+             << " positional arguments: See: " << argv[0] << " -help\n";
+    }
     ErrorParsing = true;
 
   } else if (!ConsumeAfterOpt) {
@@ -1109,8 +1316,12 @@
   MoreHelp.clear();
 
   // If we had an error processing our arguments, don't let the program execute
-  if (ErrorParsing)
-    exit(1);
+  if (ErrorParsing) {
+    if (!IgnoreErrors)
+      exit(1);
+    return false;
+  }
+  return true;
 }
 
 //===----------------------------------------------------------------------===//
@@ -1460,6 +1671,11 @@
   return strcmp(LHS->first, RHS->first);
 }
 
+static int SubNameCompare(const std::pair<const char *, SubCommand *> *LHS,
+                          const std::pair<const char *, SubCommand *> *RHS) {
+  return strcmp(LHS->first, RHS->first);
+}
+
 // Copy Options into a vector so we can sort them as we like.
 static void sortOpts(StringMap<Option *> &OptMap,
                      SmallVectorImpl<std::pair<const char *, Option *>> &Opts,
@@ -1488,6 +1704,17 @@
   array_pod_sort(Opts.begin(), Opts.end(), OptNameCompare);
 }
 
+static void
+sortSubCommands(const SmallPtrSetImpl<SubCommand *> &SubMap,
+                SmallVectorImpl<std::pair<const char *, SubCommand *>> &Subs) {
+  for (const auto &S : SubMap) {
+    if (S->getName() == nullptr)
+      continue;
+    Subs.push_back(std::make_pair(S->getName(), S));
+  }
+  array_pod_sort(Subs.begin(), Subs.end(), SubNameCompare);
+}
+
 namespace {
 
 class HelpPrinter {
@@ -1495,12 +1722,25 @@
   const bool ShowHidden;
   typedef SmallVector<std::pair<const char *, Option *>, 128>
       StrOptionPairVector;
+  typedef SmallVector<std::pair<const char *, SubCommand *>, 128>
+      StrSubCommandPairVector;
   // Print the options. Opts is assumed to be alphabetically sorted.
   virtual void printOptions(StrOptionPairVector &Opts, size_t MaxArgLen) {
     for (size_t i = 0, e = Opts.size(); i != e; ++i)
       Opts[i].second->printOptionInfo(MaxArgLen);
   }
 
+  void printSubCommands(StrSubCommandPairVector &Subs, size_t MaxSubLen) {
+    for (const auto &S : Subs) {
+      outs() << "  " << S.first;
+      if (S.second->getDescription()) {
+        outs().indent(MaxSubLen - strlen(S.first));
+        outs() << " - " << S.second->getDescription();
+      }
+      outs() << "\n";
+    }
+  }
+
 public:
   explicit HelpPrinter(bool showHidden) : ShowHidden(showHidden) {}
   virtual ~HelpPrinter() {}
@@ -1510,23 +1750,56 @@
     if (!Value)
       return;
 
+    SubCommand *Sub = GlobalParser->getActiveSubCommand();
+    auto &OptionsMap = Sub->OptionsMap;
+    auto &PositionalOpts = Sub->PositionalOpts;
+    auto &ConsumeAfterOpt = Sub->ConsumeAfterOpt;
+
     StrOptionPairVector Opts;
-    sortOpts(GlobalParser->OptionsMap, Opts, ShowHidden);
+    sortOpts(OptionsMap, Opts, ShowHidden);
+
+    StrSubCommandPairVector Subs;
+    sortSubCommands(GlobalParser->RegisteredSubCommands, Subs);
 
     if (GlobalParser->ProgramOverview)
       outs() << "OVERVIEW: " << GlobalParser->ProgramOverview << "\n";
 
-    outs() << "USAGE: " << GlobalParser->ProgramName << " [options]";
+    if (Sub == &*TopLevelSubCommand)
+      outs() << "USAGE: " << GlobalParser->ProgramName
+             << " [subcommand] [options]";
+    else {
+      if (Sub->getDescription() != nullptr) {
+        outs() << "SUBCOMMAND '" << Sub->getName()
+               << "': " << Sub->getDescription() << "\n\n";
+      }
+      outs() << "USAGE: " << GlobalParser->ProgramName << " " << Sub->getName()
+             << " [options]";
+    }
 
-    for (auto Opt : GlobalParser->PositionalOpts) {
+    for (auto Opt : PositionalOpts) {
       if (Opt->hasArgStr())
         outs() << " --" << Opt->ArgStr;
       outs() << " " << Opt->HelpStr;
     }
 
     // Print the consume after option info if it exists...
-    if (GlobalParser->ConsumeAfterOpt)
-      outs() << " " << GlobalParser->ConsumeAfterOpt->HelpStr;
+    if (ConsumeAfterOpt)
+      outs() << " " << ConsumeAfterOpt->HelpStr;
+
+    if (Sub == &*TopLevelSubCommand && Subs.size() > 2) {
+      // Compute the maximum subcommand length...
+      size_t MaxSubLen = 0;
+      for (size_t i = 0, e = Subs.size(); i != e; ++i)
+        MaxSubLen = std::max(MaxSubLen, strlen(Subs[i].first));
+
+      outs() << "\n\n";
+      outs() << "SUBCOMMANDS:\n\n";
+      printSubCommands(Subs, MaxSubLen);
+      outs() << "\n";
+      outs() << "  Type \"" << GlobalParser->ProgramName
+             << " <subcommand> -help\" to get more help on a specific "
+                "subcommand";
+    }
 
     outs() << "\n\n";
 
@@ -1675,12 +1948,13 @@
     "help-list",
     cl::desc("Display list of available options (-help-list-hidden for more)"),
     cl::location(UncategorizedNormalPrinter), cl::Hidden, cl::ValueDisallowed,
-    cl::cat(GenericCategory));
+    cl::cat(GenericCategory), cl::sub(*AllSubCommands));
 
 static cl::opt<HelpPrinter, true, parser<bool>>
     HLHOp("help-list-hidden", cl::desc("Display list of all available options"),
           cl::location(UncategorizedHiddenPrinter), cl::Hidden,
-          cl::ValueDisallowed, cl::cat(GenericCategory));
+          cl::ValueDisallowed, cl::cat(GenericCategory),
+          cl::sub(*AllSubCommands));
 
 // Define uncategorized/categorized help printers. These printers change their
 // behaviour at runtime depending on whether one or more Option categories have
@@ -1688,22 +1962,23 @@
 static cl::opt<HelpPrinterWrapper, true, parser<bool>>
     HOp("help", cl::desc("Display available options (-help-hidden for more)"),
         cl::location(WrappedNormalPrinter), cl::ValueDisallowed,
-        cl::cat(GenericCategory));
+        cl::cat(GenericCategory), cl::sub(*AllSubCommands));
 
 static cl::opt<HelpPrinterWrapper, true, parser<bool>>
     HHOp("help-hidden", cl::desc("Display all available options"),
          cl::location(WrappedHiddenPrinter), cl::Hidden, cl::ValueDisallowed,
-         cl::cat(GenericCategory));
+         cl::cat(GenericCategory), cl::sub(*AllSubCommands));
 
 static cl::opt<bool> PrintOptions(
     "print-options",
     cl::desc("Print non-default options after command line parsing"),
-    cl::Hidden, cl::init(false), cl::cat(GenericCategory));
+    cl::Hidden, cl::init(false), cl::cat(GenericCategory),
+    cl::sub(*AllSubCommands));
 
 static cl::opt<bool> PrintAllOptions(
     "print-all-options",
     cl::desc("Print all option values after command line parsing"), cl::Hidden,
-    cl::init(false), cl::cat(GenericCategory));
+    cl::init(false), cl::cat(GenericCategory), cl::sub(*AllSubCommands));
 
 void HelpPrinterWrapper::operator=(bool Value) {
   if (!Value)
@@ -1730,7 +2005,7 @@
     return;
 
   SmallVector<std::pair<const char *, Option *>, 128> Opts;
-  sortOpts(OptionsMap, Opts, /*ShowHidden*/ true);
+  sortOpts(ActiveSubCommand->OptionsMap, Opts, /*ShowHidden*/ true);
 
   // Compute the maximum argument length...
   size_t MaxArgLen = 0;
@@ -1839,22 +2114,25 @@
   ExtraVersionPrinters->push_back(func);
 }
 
-StringMap<Option *> &cl::getRegisteredOptions() {
-  return GlobalParser->OptionsMap;
+StringMap<Option *> &cl::getRegisteredOptions(SubCommand &Sub) {
+  auto &Subs = GlobalParser->RegisteredSubCommands;
+  assert(std::find(Subs.begin(), Subs.end(), &Sub) != Subs.end());
+  return Sub.OptionsMap;
 }
 
-void cl::HideUnrelatedOptions(cl::OptionCategory &Category) {
-  for (auto &I : GlobalParser->OptionsMap) {
+void cl::HideUnrelatedOptions(cl::OptionCategory &Category, SubCommand &Sub) {
+  for (auto &I : Sub.OptionsMap) {
     if (I.second->Category != &Category &&
         I.second->Category != &GenericCategory)
       I.second->setHiddenFlag(cl::ReallyHidden);
   }
 }
 
-void cl::HideUnrelatedOptions(ArrayRef<const cl::OptionCategory *> Categories) {
+void cl::HideUnrelatedOptions(ArrayRef<const cl::OptionCategory *> Categories,
+                              SubCommand &Sub) {
   auto CategoriesBegin = Categories.begin();
   auto CategoriesEnd = Categories.end();
-  for (auto &I : GlobalParser->OptionsMap) {
+  for (auto &I : Sub.OptionsMap) {
     if (std::find(CategoriesBegin, CategoriesEnd, I.second->Category) ==
             CategoriesEnd &&
         I.second->Category != &GenericCategory)
@@ -1862,7 +2140,9 @@
   }
 }
 
+void cl::ResetCommandLineOptions() { GlobalParser->reset(); }
+
 void LLVMParseCommandLineOptions(int argc, const char *const *argv,
                                  const char *Overview) {
-  llvm::cl::ParseCommandLineOptions(argc, argv, Overview);
+  llvm::cl::ParseCommandLineOptions(argc, argv, Overview, true);
 }
Index: llvm/trunk/unittests/Support/CommandLineTest.cpp
===================================================================
--- llvm/trunk/unittests/Support/CommandLineTest.cpp
+++ llvm/trunk/unittests/Support/CommandLineTest.cpp
@@ -67,6 +67,22 @@
     : Base(M0, M1, M2, M3) {}
 
   ~StackOption() override { this->removeArgument(); }
+
+  template <class DT> StackOption<T> &operator=(const DT &V) {
+    this->setValue(V);
+    return *this;
+  }
+};
+
+class StackSubCommand : public cl::SubCommand {
+public:
+  StackSubCommand(const char *const Name,
+                  const char *const Description = nullptr)
+      : SubCommand(Name, Description) {}
+
+  StackSubCommand() : SubCommand() {}
+
+  ~StackSubCommand() { unregisterSubCommand(); }
 };
 
 
@@ -78,7 +94,8 @@
   const char ArgString[] = "new-test-option";
   const char ValueString[] = "Integer";
 
-  StringMap<cl::Option *> &Map = cl::getRegisteredOptions();
+  StringMap<cl::Option *> &Map =
+      cl::getRegisteredOptions(*cl::TopLevelSubCommand);
 
   ASSERT_TRUE(Map.count("test-option") == 1) <<
     "Could not find option in map.";
@@ -237,7 +254,8 @@
   ASSERT_EQ(cl::NotHidden, TestOption2.getOptionHiddenFlag())
       << "Hid extra option that should be visable.";
 
-  StringMap<cl::Option *> &Map = cl::getRegisteredOptions();
+  StringMap<cl::Option *> &Map =
+      cl::getRegisteredOptions(*cl::TopLevelSubCommand);
   ASSERT_EQ(cl::NotHidden, Map["help"]->getOptionHiddenFlag())
       << "Hid default option that should be visable.";
 }
@@ -261,9 +279,189 @@
   ASSERT_EQ(cl::NotHidden, TestOption3.getOptionHiddenFlag())
       << "Hid extra option that should be visable.";
 
-  StringMap<cl::Option *> &Map = cl::getRegisteredOptions();
+  StringMap<cl::Option *> &Map =
+      cl::getRegisteredOptions(*cl::TopLevelSubCommand);
   ASSERT_EQ(cl::NotHidden, Map["help"]->getOptionHiddenFlag())
       << "Hid default option that should be visable.";
 }
 
+TEST(CommandLineTest, SetValueInSubcategories) {
+  cl::ResetCommandLineOptions();
+
+  StackSubCommand SC1("sc1", "First subcommand");
+  StackSubCommand SC2("sc2", "Second subcommand");
+
+  StackOption<bool> TopLevelOpt("top-level", cl::init(false));
+  StackOption<bool> SC1Opt("sc1", cl::sub(SC1), cl::init(false));
+  StackOption<bool> SC2Opt("sc2", cl::sub(SC2), cl::init(false));
+
+  EXPECT_FALSE(TopLevelOpt);
+  EXPECT_FALSE(SC1Opt);
+  EXPECT_FALSE(SC2Opt);
+  const char *args[] = {"prog", "-top-level"};
+  EXPECT_TRUE(cl::ParseCommandLineOptions(2, args, nullptr, true));
+  EXPECT_TRUE(TopLevelOpt);
+  EXPECT_FALSE(SC1Opt);
+  EXPECT_FALSE(SC2Opt);
+
+  TopLevelOpt = false;
+
+  EXPECT_FALSE(TopLevelOpt);
+  EXPECT_FALSE(SC1Opt);
+  EXPECT_FALSE(SC2Opt);
+  const char *args2[] = {"prog", "sc1", "-sc1"};
+  EXPECT_TRUE(cl::ParseCommandLineOptions(3, args2, nullptr, true));
+  EXPECT_FALSE(TopLevelOpt);
+  EXPECT_TRUE(SC1Opt);
+  EXPECT_FALSE(SC2Opt);
+
+  SC1Opt = false;
+
+  EXPECT_FALSE(TopLevelOpt);
+  EXPECT_FALSE(SC1Opt);
+  EXPECT_FALSE(SC2Opt);
+  const char *args3[] = {"prog", "sc2", "-sc2"};
+  EXPECT_TRUE(cl::ParseCommandLineOptions(3, args3, nullptr, true));
+  EXPECT_FALSE(TopLevelOpt);
+  EXPECT_FALSE(SC1Opt);
+  EXPECT_TRUE(SC2Opt);
+}
+
+TEST(CommandLineTest, LookupFailsInWrongSubCommand) {
+  cl::ResetCommandLineOptions();
+
+  StackSubCommand SC1("sc1", "First subcommand");
+  StackSubCommand SC2("sc2", "Second subcommand");
+
+  StackOption<bool> SC1Opt("sc1", cl::sub(SC1), cl::init(false));
+  StackOption<bool> SC2Opt("sc2", cl::sub(SC2), cl::init(false));
+
+  const char *args[] = {"prog", "sc1", "-sc2"};
+  EXPECT_FALSE(cl::ParseCommandLineOptions(3, args, nullptr, true));
+}
+
+TEST(CommandLineTest, AddToAllSubCommands) {
+  cl::ResetCommandLineOptions();
+
+  StackSubCommand SC1("sc1", "First subcommand");
+  StackOption<bool> AllOpt("everywhere", cl::sub(*cl::AllSubCommands),
+                           cl::init(false));
+  StackSubCommand SC2("sc2", "Second subcommand");
+
+  const char *args[] = {"prog", "-everywhere"};
+  const char *args2[] = {"prog", "sc1", "-everywhere"};
+  const char *args3[] = {"prog", "sc2", "-everywhere"};
+
+  EXPECT_FALSE(AllOpt);
+  EXPECT_TRUE(cl::ParseCommandLineOptions(2, args, nullptr, true));
+  EXPECT_TRUE(AllOpt);
+
+  AllOpt = false;
+
+  EXPECT_FALSE(AllOpt);
+  EXPECT_TRUE(cl::ParseCommandLineOptions(3, args2, nullptr, true));
+  EXPECT_TRUE(AllOpt);
+
+  AllOpt = false;
+
+  EXPECT_FALSE(AllOpt);
+  EXPECT_TRUE(cl::ParseCommandLineOptions(3, args3, nullptr, true));
+  EXPECT_TRUE(AllOpt);
+}
+
+TEST(CommandLineTest, ReparseCommandLineOptions) {
+  cl::ResetCommandLineOptions();
+
+  StackOption<bool> TopLevelOpt("top-level", cl::sub(*cl::TopLevelSubCommand),
+                                cl::init(false));
+
+  const char *args[] = {"prog", "-top-level"};
+
+  EXPECT_FALSE(TopLevelOpt);
+  EXPECT_TRUE(cl::ParseCommandLineOptions(2, args, nullptr, true));
+  EXPECT_TRUE(TopLevelOpt);
+
+  TopLevelOpt = false;
+
+  EXPECT_FALSE(TopLevelOpt);
+  EXPECT_TRUE(cl::ParseCommandLineOptions(2, args, nullptr, true));
+  EXPECT_TRUE(TopLevelOpt);
+}
+
+TEST(CommandLineTest, RemoveFromRegularSubCommand) {
+  cl::ResetCommandLineOptions();
+
+  StackSubCommand SC("sc", "Subcommand");
+  StackOption<bool> RemoveOption("remove-option", cl::sub(SC), cl::init(false));
+  StackOption<bool> KeepOption("keep-option", cl::sub(SC), cl::init(false));
+
+  const char *args[] = {"prog", "sc", "-remove-option"};
+
+  EXPECT_FALSE(RemoveOption);
+  EXPECT_TRUE(cl::ParseCommandLineOptions(3, args, nullptr, true));
+  EXPECT_TRUE(RemoveOption);
+
+  RemoveOption.removeArgument();
+
+  EXPECT_FALSE(cl::ParseCommandLineOptions(3, args, nullptr, true));
+}
+
+TEST(CommandLineTest, RemoveFromTopLevelSubCommand) {
+  cl::ResetCommandLineOptions();
+
+  StackOption<bool> TopLevelRemove(
+      "top-level-remove", cl::sub(*cl::TopLevelSubCommand), cl::init(false));
+  StackOption<bool> TopLevelKeep(
+      "top-level-keep", cl::sub(*cl::TopLevelSubCommand), cl::init(false));
+
+  const char *args[] = {"prog", "-top-level-remove"};
+
+  EXPECT_FALSE(TopLevelRemove);
+  EXPECT_TRUE(cl::ParseCommandLineOptions(2, args, nullptr, true));
+  EXPECT_TRUE(TopLevelRemove);
+
+  TopLevelRemove.removeArgument();
+
+  EXPECT_FALSE(cl::ParseCommandLineOptions(2, args, nullptr, true));
+}
+
+TEST(CommandLineTest, RemoveFromAllSubCommands) {
+  cl::ResetCommandLineOptions();
+
+  StackSubCommand SC1("sc1", "First Subcommand");
+  StackSubCommand SC2("sc2", "Second Subcommand");
+  StackOption<bool> RemoveOption("remove-option", cl::sub(*cl::AllSubCommands),
+                                 cl::init(false));
+  StackOption<bool> KeepOption("keep-option", cl::sub(*cl::AllSubCommands),
+                               cl::init(false));
+
+  const char *args0[] = {"prog", "-remove-option"};
+  const char *args1[] = {"prog", "sc1", "-remove-option"};
+  const char *args2[] = {"prog", "sc2", "-remove-option"};
+
+  // It should work for all subcommands including the top-level.
+  EXPECT_FALSE(RemoveOption);
+  EXPECT_TRUE(cl::ParseCommandLineOptions(2, args0, nullptr, true));
+  EXPECT_TRUE(RemoveOption);
+
+  RemoveOption = false;
+
+  EXPECT_FALSE(RemoveOption);
+  EXPECT_TRUE(cl::ParseCommandLineOptions(3, args1, nullptr, true));
+  EXPECT_TRUE(RemoveOption);
+
+  RemoveOption = false;
+
+  EXPECT_FALSE(RemoveOption);
+  EXPECT_TRUE(cl::ParseCommandLineOptions(3, args2, nullptr, true));
+  EXPECT_TRUE(RemoveOption);
+
+  RemoveOption.removeArgument();
+
+  // It should not work for any subcommands including the top-level.
+  EXPECT_FALSE(cl::ParseCommandLineOptions(2, args0, nullptr, true));
+  EXPECT_FALSE(cl::ParseCommandLineOptions(3, args1, nullptr, true));
+  EXPECT_FALSE(cl::ParseCommandLineOptions(3, args2, nullptr, true));
+}
+
 }  // anonymous namespace
Index: llvm/trunk/unittests/Support/ProgramTest.cpp
===================================================================
--- llvm/trunk/unittests/Support/ProgramTest.cpp
+++ llvm/trunk/unittests/Support/ProgramTest.cpp
@@ -231,7 +231,7 @@
   // LoopCount should only be incremented once.
   while (true) {
     ++LoopCount;
-    ProcessInfo WaitResult = Wait(PI1, 0, true, &Error);
+    ProcessInfo WaitResult = llvm::sys::Wait(PI1, 0, true, &Error);
     ASSERT_TRUE(Error.empty());
     if (WaitResult.Pid == PI1.Pid)
       break;
@@ -248,7 +248,7 @@
   // cse, LoopCount should be greater than 1 (more than one increment occurs).
   while (true) {
     ++LoopCount;
-    ProcessInfo WaitResult = Wait(PI2, 0, false, &Error);
+    ProcessInfo WaitResult = llvm::sys::Wait(PI2, 0, false, &Error);
     ASSERT_TRUE(Error.empty());
     if (WaitResult.Pid == PI2.Pid)
       break;