Update clang, llvm, lld, lldb, compiler-rt and libc++ to 4.0.0 release:

MFC r309142 (by emaste):

Add WITH_LLD_AS_LD build knob

If set it installs LLD as /usr/bin/ld.  LLD (as of version 3.9) is not
capable of linking the world and kernel, but can self-host and link many
substantial applications. GNU ld continues to be used for the world and
kernel build, regardless of how this knob is set.

It is on by default for arm64, and off for all other CPU architectures.

Sponsored by:	The FreeBSD Foundation

MFC r310840:

Reapply 310775, now it also builds correctly if lldb is disabled:

Move llvm-objdump from CLANG_EXTRAS to installed by default

We currently install three tools from binutils 2.17.50: as, ld, and
objdump. Work is underway to migrate to a permissively-licensed
tool-chain, with one goal being the retirement of binutils 2.17.50.

LLVM's llvm-objdump is intended to be compatible with GNU objdump
although it is currently missing some options and may have formatting
differences. Enable it by default for testing and further investigation.
It may later be changed to install as /usr/bin/objdump, it becomes a
fully viable replacement.

Reviewed by:	emaste
Differential Revision:	https://reviews.freebsd.org/D8879

MFC r312855 (by emaste):

Rename LLD_AS_LD to LLD_IS_LD, for consistency with CLANG_IS_CC

Reported by:	Dan McGregor <dan.mcgregor usask.ca>

MFC r313559 | glebius | 2017-02-10 18:34:48 +0100 (Fri, 10 Feb 2017) | 5 lines

Don't check struct rtentry on FreeBSD, it is an internal kernel structure.
On other systems it may be API structure for SIOCADDRT/SIOCDELRT.

Reviewed by:	emaste, dim

MFC r314152 (by jkim):

Remove an assembler flag, which is redundant since r309124.  The upstream
took care of it by introducing a macro NO_EXEC_STACK_DIRECTIVE.

http://llvm.org/viewvc/llvm-project?rev=273500&view=rev

Reviewed by:	dim

MFC r314564:

Upgrade our copies of clang, llvm, lld, lldb, compiler-rt and libc++ to
4.0.0 (branches/release_40 296509).  The release will follow soon.

Please note that from 3.5.0 onwards, clang, llvm and lldb require C++11
support to build; see UPDATING for more information.

Also note that as of 4.0.0, lld should be able to link the base system
on amd64 and aarch64.  See the WITH_LLD_IS_LLD setting in src.conf(5).
Though please be aware that this is work in progress.

Release notes for llvm, clang and lld will be available here:
<http://releases.llvm.org/4.0.0/docs/ReleaseNotes.html>
<http://releases.llvm.org/4.0.0/tools/clang/docs/ReleaseNotes.html>
<http://releases.llvm.org/4.0.0/tools/lld/docs/ReleaseNotes.html>

Thanks to Ed Maste, Jan Beich, Antoine Brodin and Eric Fiselier for
their help.

Relnotes:	yes
Exp-run:	antoine
PR:		215969, 216008

MFC r314708:

For now, revert r287232 from upstream llvm trunk (by Daniil Fukalov):

  [SCEV] limit recursion depth of CompareSCEVComplexity

  Summary:
  CompareSCEVComplexity goes too deep (50+ on a quite a big unrolled
  loop) and runs almost infinite time.

  Added cache of "equal" SCEV pairs to earlier cutoff of further
  estimation. Recursion depth limit was also introduced as a parameter.

  Reviewers: sanjoy

  Subscribers: mzolotukhin, tstellarAMD, llvm-commits

  Differential Revision: https://reviews.llvm.org/D26389

This commit is the cause of excessive compile times on skein_block.c
(and possibly other files) during kernel builds on amd64.

We never saw the problematic behavior described in this upstream commit,
so for now it is better to revert it.  An upstream bug has been filed
here: https://bugs.llvm.org/show_bug.cgi?id=32142

Reported by:	mjg

MFC r314795:

Reapply r287232 from upstream llvm trunk (by Daniil Fukalov):

  [SCEV] limit recursion depth of CompareSCEVComplexity

  Summary:
  CompareSCEVComplexity goes too deep (50+ on a quite a big unrolled
  loop) and runs almost infinite time.

  Added cache of "equal" SCEV pairs to earlier cutoff of further
  estimation. Recursion depth limit was also introduced as a parameter.

  Reviewers: sanjoy

  Subscribers: mzolotukhin, tstellarAMD, llvm-commits

  Differential Revision: https://reviews.llvm.org/D26389

Pull in r296992 from upstream llvm trunk (by Sanjoy Das):

  [SCEV] Decrease the recursion threshold for CompareValueComplexity

  Fixes PR32142.

  r287232 accidentally increased the recursion threshold for
  CompareValueComplexity from 2 to 32.  This change reverses that
  change by introducing a separate flag for CompareValueComplexity's
  threshold.

The latter revision fixes the excessive compile times for skein_block.c.

MFC r314907 | mmel | 2017-03-08 12:40:27 +0100 (Wed, 08 Mar 2017) | 7 lines

Unbreak ARMv6 world.

The new compiler_rt library imported with clang 4.0.0 have several fatal
issues (non-functional __udivsi3 for example) with ARM specific instrict
functions. As temporary workaround, until upstream solve these problems,
disable all thumb[1][2] related feature.

MFC r315016:

Update clang, llvm, lld, lldb, compiler-rt and libc++ to 4.0.0 release.
We were already very close to the last release candidate, so this is a
pretty minor update.

Relnotes:	yes

MFC r316005:

Revert r314907, and pull in r298713 from upstream compiler-rt trunk (by
Weiming Zhao):

  builtins: Select correct code fragments when compiling for Thumb1/Thum2/ARM ISA.

  Summary:
  Value of __ARM_ARCH_ISA_THUMB isn't based on the actual compilation
  mode (-mthumb, -marm), it reflect's capability of given CPU.

  Due to this:
   - use  __tbumb__ and __thumb2__ insteand of __ARM_ARCH_ISA_THUMB
   - use '.thumb' directive consistently  in all affected files
   - decorate all thumb functions using
     DEFINE_COMPILERRT_THUMB_FUNCTION()

  ---------
  Note: This patch doesn't fix broken Thumb1 variant of __udivsi3 !

  Reviewers: weimingz, rengolin, compnerd

  Subscribers: aemerson, dim

  Differential Revision: https://reviews.llvm.org/D30938

Discussed with:	mmel

1 files changed, 123 insertions, 90 deletions

diff --git a/contrib/llvm/lib/Support/CommandLine.cpp b/contrib/llvm/lib/Support/CommandLine.cpp
index a5d2ba2..3889902 100644
--- a/contrib/llvm/lib/Support/CommandLine.cpp
+++ b/contrib/llvm/lib/Support/CommandLine.cpp
@@ -20,6 +20,7 @@
 #include "llvm-c/Support.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/Optional.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/SmallString.h"
@@ -29,10 +30,12 @@
 #include "llvm/Support/ConvertUTF.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Host.h"
 #include "llvm/Support/ManagedStatic.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/Path.h"
+#include "llvm/Support/Process.h"
 #include "llvm/Support/StringSaver.h"
 #include "llvm/Support/raw_ostream.h"
 #include <cstdlib>
@@ -42,6 +45,17 @@ using namespace cl;
 
 #define DEBUG_TYPE "commandline"
 
+#if LLVM_ENABLE_ABI_BREAKING_CHECKS
+namespace llvm {
+// If LLVM_ENABLE_ABI_BREAKING_CHECKS is set the flag -mllvm -reverse-iterate
+// can be used to toggle forward/reverse iteration of unordered containers.
+// This will help uncover differences in codegen caused due to undefined
+// iteration order.
+static cl::opt<bool, true> ReverseIteration("reverse-iterate",
+  cl::location(ReverseIterate<bool>::value));
+}
+#endif
+
 //===----------------------------------------------------------------------===//
 // Template instantiations and anchors.
 //
@@ -90,10 +104,10 @@ public:
   // Globals for name and overview of program.  Program name is not a string to
   // avoid static ctor/dtor issues.
   std::string ProgramName;
-  const char *ProgramOverview;
+  StringRef ProgramOverview;
 
   // This collects additional help to be printed.
-  std::vector<const char *> MoreHelp;
+  std::vector<StringRef> MoreHelp;
 
   // This collects the different option categories that have been registered.
   SmallPtrSet<OptionCategory *, 16> RegisteredOptionCategories;
@@ -101,7 +115,7 @@ public:
   // This collects the different subcommands that have been registered.
   SmallPtrSet<SubCommand *, 4> RegisteredSubCommands;
 
-  CommandLineParser() : ProgramOverview(nullptr), ActiveSubCommand(nullptr) {
+  CommandLineParser() : ActiveSubCommand(nullptr) {
     registerSubCommand(&*TopLevelSubCommand);
     registerSubCommand(&*AllSubCommands);
   }
@@ -109,9 +123,9 @@ public:
   void ResetAllOptionOccurrences();
 
   bool ParseCommandLineOptions(int argc, const char *const *argv,
-                               const char *Overview, bool IgnoreErrors);
+                               StringRef Overview, bool IgnoreErrors);
 
-  void addLiteralOption(Option &Opt, SubCommand *SC, const char *Name) {
+  void addLiteralOption(Option &Opt, SubCommand *SC, StringRef Name) {
     if (Opt.hasArgStr())
       return;
     if (!SC->OptionsMap.insert(std::make_pair(Name, &Opt)).second) {
@@ -131,7 +145,7 @@ public:
     }
   }
 
-  void addLiteralOption(Option &Opt, const char *Name) {
+  void addLiteralOption(Option &Opt, StringRef Name) {
     if (Opt.Subs.empty())
       addLiteralOption(Opt, &*TopLevelSubCommand, Name);
     else {
@@ -283,7 +297,7 @@ public:
   void registerSubCommand(SubCommand *sub) {
     assert(count_if(RegisteredSubCommands,
                     [sub](const SubCommand *Sub) {
-                      return (sub->getName() != nullptr) &&
+                      return (!sub->getName().empty()) &&
                              (Sub->getName() == sub->getName());
                     }) == 0 &&
            "Duplicate subcommands");
@@ -298,7 +312,7 @@ public:
             O->hasArgStr())
           addOption(O, sub);
         else
-          addLiteralOption(*O, sub, E.first().str().c_str());
+          addLiteralOption(*O, sub, E.first());
       }
     }
   }
@@ -307,10 +321,16 @@ public:
     RegisteredSubCommands.erase(sub);
   }
 
+  iterator_range<typename SmallPtrSet<SubCommand *, 4>::iterator>
+  getRegisteredSubcommands() {
+    return make_range(RegisteredSubCommands.begin(),
+                      RegisteredSubCommands.end());
+  }
+
   void reset() {
     ActiveSubCommand = nullptr;
     ProgramName.clear();
-    ProgramOverview = nullptr;
+    ProgramOverview = StringRef();
 
     MoreHelp.clear();
     RegisteredOptionCategories.clear();
@@ -328,18 +348,18 @@ private:
   SubCommand *ActiveSubCommand;
 
   Option *LookupOption(SubCommand &Sub, StringRef &Arg, StringRef &Value);
-  SubCommand *LookupSubCommand(const char *Name);
+  SubCommand *LookupSubCommand(StringRef Name);
 };
 
 } // namespace
 
 static ManagedStatic<CommandLineParser> GlobalParser;
 
-void cl::AddLiteralOption(Option &O, const char *Name) {
+void cl::AddLiteralOption(Option &O, StringRef Name) {
   GlobalParser->addLiteralOption(O, Name);
 }
 
-extrahelp::extrahelp(const char *Help) : morehelp(Help) {
+extrahelp::extrahelp(StringRef Help) : morehelp(Help) {
   GlobalParser->MoreHelp.push_back(Help);
 }
 
@@ -353,6 +373,7 @@ void Option::removeArgument() { GlobalParser->removeOption(this); }
 void Option::setArgStr(StringRef S) {
   if (FullyInitialized)
     GlobalParser->updateArgStr(this, S);
+  assert((S.empty() || S[0] != '-') && "Option can't start with '-");
   ArgStr = S;
 }
 
@@ -426,13 +447,13 @@ Option *CommandLineParser::LookupOption(SubCommand &Sub, StringRef &Arg,
   return I->second;
 }
 
-SubCommand *CommandLineParser::LookupSubCommand(const char *Name) {
-  if (Name == nullptr)
+SubCommand *CommandLineParser::LookupSubCommand(StringRef Name) {
+  if (Name.empty())
     return &*TopLevelSubCommand;
   for (auto S : RegisteredSubCommands) {
     if (S == &*AllSubCommands)
       continue;
-    if (S->getName() == nullptr)
+    if (S->getName().empty())
       continue;
 
     if (StringRef(S->getName()) == StringRef(Name))
@@ -505,7 +526,6 @@ static bool CommaSeparateAndAddOccurrence(Option *Handler, unsigned pos,
         return true;
       // Erase the portion before the comma, AND the comma.
       Val = Val.substr(Pos + 1);
-      Value.substr(Pos + 1); // Increment the original value pointer as well.
       // Check for another comma.
       Pos = Val.find(',');
     }
@@ -533,7 +553,7 @@ static inline bool ProvideOption(Option *Handler, StringRef ArgName,
         return Handler->error("requires a value!");
       // Steal the next argument, like for '-o filename'
       assert(argv && "null check");
-      Value = argv[++i];
+      Value = StringRef(argv[++i]);
     }
     break;
   case ValueDisallowed:
@@ -567,7 +587,7 @@ static inline bool ProvideOption(Option *Handler, StringRef ArgName,
     if (i + 1 >= argc)
       return Handler->error("not enough values!");
     assert(argv && "null check");
-    Value = argv[++i];
+    Value = StringRef(argv[++i]);
 
     if (CommaSeparateAndAddOccurrence(Handler, i, ArgName, Value, MultiArg))
       return true;
@@ -725,7 +745,7 @@ void cl::TokenizeGNUCommandLine(StringRef Src, StringSaver &Saver,
     // End the token if this is whitespace.
     if (isWhitespace(Src[I])) {
       if (!Token.empty())
-        NewArgv.push_back(Saver.save(Token.c_str()));
+        NewArgv.push_back(Saver.save(StringRef(Token)).data());
       Token.clear();
       continue;
     }
@@ -736,7 +756,7 @@ void cl::TokenizeGNUCommandLine(StringRef Src, StringSaver &Saver,
 
   // Append the last token after hitting EOF with no whitespace.
   if (!Token.empty())
-    NewArgv.push_back(Saver.save(Token.c_str()));
+    NewArgv.push_back(Saver.save(StringRef(Token)).data());
   // Mark the end of response files
   if (MarkEOLs)
     NewArgv.push_back(nullptr);
@@ -817,7 +837,7 @@ void cl::TokenizeWindowsCommandLine(StringRef Src, StringSaver &Saver,
     if (State == UNQUOTED) {
       // Whitespace means the end of the token.
       if (isWhitespace(Src[I])) {
-        NewArgv.push_back(Saver.save(Token.c_str()));
+        NewArgv.push_back(Saver.save(StringRef(Token)).data());
         Token.clear();
         State = INIT;
         // Mark the end of lines in response files
@@ -852,7 +872,7 @@ void cl::TokenizeWindowsCommandLine(StringRef Src, StringSaver &Saver,
   }
   // Append the last token after hitting EOF with no whitespace.
   if (!Token.empty())
-    NewArgv.push_back(Saver.save(Token.c_str()));
+    NewArgv.push_back(Saver.save(StringRef(Token)).data());
   // Mark the end of response files
   if (MarkEOLs)
     NewArgv.push_back(nullptr);
@@ -864,10 +884,10 @@ static bool hasUTF8ByteOrderMark(ArrayRef<char> S) {
   return (S.size() >= 3 && S[0] == '\xef' && S[1] == '\xbb' && S[2] == '\xbf');
 }
 
-static bool ExpandResponseFile(const char *FName, StringSaver &Saver,
+static bool ExpandResponseFile(StringRef FName, StringSaver &Saver,
                                TokenizerCallback Tokenizer,
                                SmallVectorImpl<const char *> &NewArgv,
-                               bool MarkEOLs = false) {
+                               bool MarkEOLs, bool RelativeNames) {
   ErrorOr<std::unique_ptr<MemoryBuffer>> MemBufOrErr =
       MemoryBuffer::getFile(FName);
   if (!MemBufOrErr)
@@ -892,6 +912,30 @@ static bool ExpandResponseFile(const char *FName, StringSaver &Saver,
   // Tokenize the contents into NewArgv.
   Tokenizer(Str, Saver, NewArgv, MarkEOLs);
 
+  // If names of nested response files should be resolved relative to including
+  // file, replace the included response file names with their full paths
+  // obtained by required resolution.
+  if (RelativeNames)
+    for (unsigned I = 0; I < NewArgv.size(); ++I)
+      if (NewArgv[I]) {
+        StringRef Arg = NewArgv[I];
+        if (Arg.front() == '@') {
+          StringRef FileName = Arg.drop_front();
+          if (llvm::sys::path::is_relative(FileName)) {
+            SmallString<128> ResponseFile;
+            ResponseFile.append(1, '@');
+            if (llvm::sys::path::is_relative(FName)) {
+              SmallString<128> curr_dir;
+              llvm::sys::fs::current_path(curr_dir);
+              ResponseFile.append(curr_dir.str());
+            }
+            llvm::sys::path::append(
+                ResponseFile, llvm::sys::path::parent_path(FName), FileName);
+            NewArgv[I] = Saver.save(ResponseFile.c_str()).data();
+          }
+        }
+      }
+
   return true;
 }
 
@@ -899,7 +943,7 @@ static bool ExpandResponseFile(const char *FName, StringSaver &Saver,
 /// StringSaver and tokenization strategy.
 bool cl::ExpandResponseFiles(StringSaver &Saver, TokenizerCallback Tokenizer,
                              SmallVectorImpl<const char *> &Argv,
-                             bool MarkEOLs) {
+                             bool MarkEOLs, bool RelativeNames) {
   unsigned RspFiles = 0;
   bool AllExpanded = true;
 
@@ -923,11 +967,9 @@ bool cl::ExpandResponseFiles(StringSaver &Saver, TokenizerCallback Tokenizer,
 
     // Replace this response file argument with the tokenization of its
     // contents.  Nested response files are expanded in subsequent iterations.
-    // FIXME: If a nested response file uses a relative path, is it relative to
-    // the cwd of the process or the response file?
     SmallVector<const char *, 0> ExpandedArgv;
     if (!ExpandResponseFile(Arg + 1, Saver, Tokenizer, ExpandedArgv,
-                            MarkEOLs)) {
+                            MarkEOLs, RelativeNames)) {
       // We couldn't read this file, so we leave it in the argument stream and
       // move on.
       AllExpanded = false;
@@ -952,45 +994,26 @@ void cl::ParseEnvironmentOptions(const char *progName, const char *envVar,
   assert(envVar && "Environment variable name missing");
 
   // Get the environment variable they want us to parse options out of.
-#ifdef _WIN32
-  std::wstring wenvVar;
-  if (!llvm::ConvertUTF8toWide(envVar, wenvVar)) {
-    assert(false &&
-           "Unicode conversion of environment variable name failed");
-    return;
-  }
-  const wchar_t *wenvValue = _wgetenv(wenvVar.c_str());
-  if (!wenvValue)
-    return;
-  std::string envValueBuffer;
-  if (!llvm::convertWideToUTF8(wenvValue, envValueBuffer)) {
-    assert(false &&
-           "Unicode conversion of environment variable value failed");
-    return;
-  }
-  const char *envValue = envValueBuffer.c_str();
-#else
-  const char *envValue = getenv(envVar);
+  llvm::Optional<std::string> envValue = sys::Process::GetEnv(StringRef(envVar));
   if (!envValue)
     return;
-#endif
 
   // Get program's "name", which we wouldn't know without the caller
   // telling us.
   SmallVector<const char *, 20> newArgv;
   BumpPtrAllocator A;
   StringSaver Saver(A);
-  newArgv.push_back(Saver.save(progName));
+  newArgv.push_back(Saver.save(progName).data());
 
   // Parse the value of the environment variable into a "command line"
   // and hand it off to ParseCommandLineOptions().
-  TokenizeGNUCommandLine(envValue, Saver, newArgv);
+  TokenizeGNUCommandLine(*envValue, Saver, newArgv);
   int newArgc = static_cast<int>(newArgv.size());
-  ParseCommandLineOptions(newArgc, &newArgv[0], Overview);
+  ParseCommandLineOptions(newArgc, &newArgv[0], StringRef(Overview));
 }
 
 bool cl::ParseCommandLineOptions(int argc, const char *const *argv,
-                                 const char *Overview, bool IgnoreErrors) {
+                                 StringRef Overview, bool IgnoreErrors) {
   return GlobalParser->ParseCommandLineOptions(argc, argv, Overview,
                                                IgnoreErrors);
 }
@@ -1006,7 +1029,7 @@ void CommandLineParser::ResetAllOptionOccurrences() {
 
 bool CommandLineParser::ParseCommandLineOptions(int argc,
                                                 const char *const *argv,
-                                                const char *Overview,
+                                                StringRef Overview,
                                                 bool IgnoreErrors) {
   assert(hasOptions() && "No options specified!");
 
@@ -1019,7 +1042,7 @@ bool CommandLineParser::ParseCommandLineOptions(int argc,
   argc = static_cast<int>(newArgv.size());
 
   // Copy the program name into ProgName, making sure not to overflow it.
-  ProgramName = sys::path::filename(argv[0]);
+  ProgramName = sys::path::filename(StringRef(argv[0]));
 
   ProgramOverview = Overview;
   bool ErrorParsing = false;
@@ -1035,7 +1058,7 @@ bool CommandLineParser::ParseCommandLineOptions(int argc,
   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]);
+    ChosenSubCommand = LookupSubCommand(StringRef(argv[FirstArg]));
     if (ChosenSubCommand != &*TopLevelSubCommand)
       FirstArg = 2;
   }
@@ -1116,19 +1139,19 @@ bool CommandLineParser::ParseCommandLineOptions(int argc,
     if (argv[i][0] != '-' || argv[i][1] == 0 || DashDashFound) {
       // Positional argument!
       if (ActivePositionalArg) {
-        ProvidePositionalOption(ActivePositionalArg, argv[i], i);
+        ProvidePositionalOption(ActivePositionalArg, StringRef(argv[i]), i);
         continue; // We are done!
       }
 
       if (!PositionalOpts.empty()) {
-        PositionalVals.push_back(std::make_pair(argv[i], i));
+        PositionalVals.push_back(std::make_pair(StringRef(argv[i]), i));
 
         // All of the positional arguments have been fulfulled, give the rest to
         // the consume after option... if it's specified...
         //
         if (PositionalVals.size() >= NumPositionalRequired && ConsumeAfterOpt) {
           for (++i; i < argc; ++i)
-            PositionalVals.push_back(std::make_pair(argv[i], i));
+            PositionalVals.push_back(std::make_pair(StringRef(argv[i]), i));
           break; // Handle outside of the argument processing loop...
         }
 
@@ -1144,19 +1167,19 @@ bool CommandLineParser::ParseCommandLineOptions(int argc,
       // If there is a positional argument eating options, check to see if this
       // option is another positional argument.  If so, treat it as an argument,
       // otherwise feed it to the eating positional.
-      ArgName = argv[i] + 1;
+      ArgName = StringRef(argv[i] + 1);
       // Eat leading dashes.
       while (!ArgName.empty() && ArgName[0] == '-')
         ArgName = ArgName.substr(1);
 
       Handler = LookupOption(*ChosenSubCommand, ArgName, Value);
       if (!Handler || Handler->getFormattingFlag() != cl::Positional) {
-        ProvidePositionalOption(ActivePositionalArg, argv[i], i);
+        ProvidePositionalOption(ActivePositionalArg, StringRef(argv[i]), i);
         continue; // We are done!
       }
 
     } else { // We start with a '-', must be an argument.
-      ArgName = argv[i] + 1;
+      ArgName = StringRef(argv[i] + 1);
       // Eat leading dashes.
       while (!ArgName.empty() && ArgName[0] == '-')
         ArgName = ArgName.substr(1);
@@ -1193,7 +1216,7 @@ bool CommandLineParser::ParseCommandLineOptions(int argc,
         for (SmallVectorImpl<Option *>::iterator I = SinkOpts.begin(),
                                                  E = SinkOpts.end();
              I != E; ++I)
-          (*I)->addOccurrence(i, "", argv[i]);
+          (*I)->addOccurrence(i, "", StringRef(argv[i]));
       }
       continue;
     }
@@ -1212,7 +1235,8 @@ bool CommandLineParser::ParseCommandLineOptions(int argc,
       errs() << ProgramName
              << ": Not enough positional command line arguments specified!\n"
              << "Must specify at least " << NumPositionalRequired
-             << " positional arguments: See: " << argv[0] << " -help\n";
+             << " positional argument" << (NumPositionalRequired > 1 ? "s" : "")
+             << ": See: " << argv[0] << " - help\n";
     }
 
     ErrorParsing = true;
@@ -1245,7 +1269,7 @@ bool CommandLineParser::ParseCommandLineOptions(int argc,
         switch (PositionalOpts[i]->getNumOccurrencesFlag()) {
         case cl::Optional:
           Done = true; // Optional arguments want _at most_ one value
-        // FALL THROUGH
+          LLVM_FALLTHROUGH;
         case cl::ZeroOrMore: // Zero or more will take all they can get...
         case cl::OneOrMore:  // One or more will take all they can get...
           ProvidePositionalOption(PositionalOpts[i],
@@ -1299,7 +1323,7 @@ bool CommandLineParser::ParseCommandLineOptions(int argc,
         Opt.second->error("must be specified at least once!");
         ErrorParsing = true;
       }
-    // Fall through
+      LLVM_FALLTHROUGH;
     default:
       break;
     }
@@ -1354,7 +1378,7 @@ bool Option::addOccurrence(unsigned pos, StringRef ArgName, StringRef Value,
   case Required:
     if (NumOccurrences > 1)
       return error("must occur exactly one time!", ArgName);
-  // Fall through
+    LLVM_FALLTHROUGH;
   case OneOrMore:
   case ZeroOrMore:
   case ConsumeAfter:
@@ -1406,7 +1430,8 @@ void alias::printOptionInfo(size_t GlobalWidth) const {
 // Return the width of the option tag for printing...
 size_t basic_parser_impl::getOptionWidth(const Option &O) const {
   size_t Len = O.ArgStr.size();
-  if (const char *ValName = getValueName())
+  auto ValName = getValueName();
+  if (!ValName.empty())
     Len += getValueStr(O, ValName).size() + 3;
 
   return Len + 6;
@@ -1419,7 +1444,8 @@ void basic_parser_impl::printOptionInfo(const Option &O,
                                         size_t GlobalWidth) const {
   outs() << "  -" << O.ArgStr;
 
-  if (const char *ValName = getValueName())
+  auto ValName = getValueName();
+  if (!ValName.empty())
     outs() << "=<" << getValueStr(O, ValName) << '>';
 
   printHelpStr(O.HelpStr, GlobalWidth, getOptionWidth(O));
@@ -1529,11 +1555,11 @@ bool parser<float>::parse(Option &O, StringRef ArgName, StringRef Arg,
 // findOption - Return the option number corresponding to the specified
 // argument string.  If the option is not found, getNumOptions() is returned.
 //
-unsigned generic_parser_base::findOption(const char *Name) {
+unsigned generic_parser_base::findOption(StringRef Name) {
   unsigned e = getNumOptions();
 
   for (unsigned i = 0; i != e; ++i) {
-    if (strcmp(getOption(i), Name) == 0)
+    if (getOption(i) == Name)
       return i;
   }
   return e;
@@ -1544,12 +1570,12 @@ size_t generic_parser_base::getOptionWidth(const Option &O) const {
   if (O.hasArgStr()) {
     size_t Size = O.ArgStr.size() + 6;
     for (unsigned i = 0, e = getNumOptions(); i != e; ++i)
-      Size = std::max(Size, std::strlen(getOption(i)) + 8);
+      Size = std::max(Size, getOption(i).size() + 8);
     return Size;
   } else {
     size_t BaseSize = 0;
     for (unsigned i = 0, e = getNumOptions(); i != e; ++i)
-      BaseSize = std::max(BaseSize, std::strlen(getOption(i)) + 8);
+      BaseSize = std::max(BaseSize, getOption(i).size() + 8);
     return BaseSize;
   }
 }
@@ -1564,7 +1590,7 @@ void generic_parser_base::printOptionInfo(const Option &O,
     printHelpStr(O.HelpStr, GlobalWidth, O.ArgStr.size() + 6);
 
     for (unsigned i = 0, e = getNumOptions(); i != e; ++i) {
-      size_t NumSpaces = GlobalWidth - strlen(getOption(i)) - 8;
+      size_t NumSpaces = GlobalWidth - getOption(i).size() - 8;
       outs() << "    =" << getOption(i);
       outs().indent(NumSpaces) << " -   " << getDescription(i) << '\n';
     }
@@ -1572,9 +1598,9 @@ void generic_parser_base::printOptionInfo(const Option &O,
     if (!O.HelpStr.empty())
       outs() << "  " << O.HelpStr << '\n';
     for (unsigned i = 0, e = getNumOptions(); i != e; ++i) {
-      const char *Option = getOption(i);
+      auto Option = getOption(i);
       outs() << "    -" << Option;
-      printHelpStr(getDescription(i), GlobalWidth, std::strlen(Option) + 8);
+      printHelpStr(getDescription(i), GlobalWidth, Option.size() + 8);
     }
   }
 }
@@ -1596,7 +1622,7 @@ void generic_parser_base::printGenericOptionDiff(
       continue;
 
     outs() << "= " << getOption(i);
-    size_t L = std::strlen(getOption(i));
+    size_t L = getOption(i).size();
     size_t NumSpaces = MaxOptWidth > L ? MaxOptWidth - L : 0;
     outs().indent(NumSpaces) << " (default: ";
     for (unsigned j = 0; j != NumOpts; ++j) {
@@ -1709,9 +1735,9 @@ static void
 sortSubCommands(const SmallPtrSetImpl<SubCommand *> &SubMap,
                 SmallVectorImpl<std::pair<const char *, SubCommand *>> &Subs) {
   for (const auto &S : SubMap) {
-    if (S->getName() == nullptr)
+    if (S->getName().empty())
       continue;
-    Subs.push_back(std::make_pair(S->getName(), S));
+    Subs.push_back(std::make_pair(S->getName().data(), S));
   }
   array_pod_sort(Subs.begin(), Subs.end(), SubNameCompare);
 }
@@ -1734,7 +1760,7 @@ protected:
   void printSubCommands(StrSubCommandPairVector &Subs, size_t MaxSubLen) {
     for (const auto &S : Subs) {
       outs() << "  " << S.first;
-      if (S.second->getDescription()) {
+      if (!S.second->getDescription().empty()) {
         outs().indent(MaxSubLen - strlen(S.first));
         outs() << " - " << S.second->getDescription();
       }
@@ -1762,14 +1788,16 @@ public:
     StrSubCommandPairVector Subs;
     sortSubCommands(GlobalParser->RegisteredSubCommands, Subs);
 
-    if (GlobalParser->ProgramOverview)
+    if (!GlobalParser->ProgramOverview.empty())
       outs() << "OVERVIEW: " << GlobalParser->ProgramOverview << "\n";
 
-    if (Sub == &*TopLevelSubCommand)
-      outs() << "USAGE: " << GlobalParser->ProgramName
-             << " [subcommand] [options]";
-    else {
-      if (Sub->getDescription() != nullptr) {
+    if (Sub == &*TopLevelSubCommand) {
+      outs() << "USAGE: " << GlobalParser->ProgramName;
+      if (Subs.size() > 2)
+        outs() << " [subcommand]";
+      outs() << " [options]";
+    } else {
+      if (!Sub->getDescription().empty()) {
         outs() << "SUBCOMMAND '" << Sub->getName()
                << "': " << Sub->getDescription() << "\n\n";
       }
@@ -1787,7 +1815,7 @@ public:
     if (ConsumeAfterOpt)
       outs() << " " << ConsumeAfterOpt->HelpStr;
 
-    if (Sub == &*TopLevelSubCommand && Subs.size() > 2) {
+    if (Sub == &*TopLevelSubCommand && !Subs.empty()) {
       // Compute the maximum subcommand length...
       size_t MaxSubLen = 0;
       for (size_t i = 0, e = Subs.size(); i != e; ++i)
@@ -1831,7 +1859,7 @@ public:
   // ordered before B's name. It returns a value greater equal zero otherwise.
   static int OptionCategoryCompare(OptionCategory *const *A,
                                    OptionCategory *const *B) {
-    return strcmp((*A)->getName(), (*B)->getName());
+    return (*A)->getName() == (*B)->getName();
   }
 
   // Make sure we inherit our base class's operator=()
@@ -1888,7 +1916,7 @@ protected:
       outs() << (*Category)->getName() << ":\n";
 
       // Check if description is set.
-      if ((*Category)->getDescription() != nullptr)
+      if (!(*Category)->getDescription().empty())
         outs() << (*Category)->getDescription() << "\n\n";
       else
         outs() << "\n";
@@ -2118,10 +2146,15 @@ void cl::AddExtraVersionPrinter(void (*func)()) {
 StringMap<Option *> &cl::getRegisteredOptions(SubCommand &Sub) {
   auto &Subs = GlobalParser->RegisteredSubCommands;
   (void)Subs;
-  assert(std::find(Subs.begin(), Subs.end(), &Sub) != Subs.end());
+  assert(is_contained(Subs, &Sub));
   return Sub.OptionsMap;
 }
 
+iterator_range<typename SmallPtrSet<SubCommand *, 4>::iterator>
+cl::getRegisteredSubcommands() {
+  return GlobalParser->getRegisteredSubcommands();
+}
+
 void cl::HideUnrelatedOptions(cl::OptionCategory &Category, SubCommand &Sub) {
   for (auto &I : Sub.OptionsMap) {
     if (I.second->Category != &Category &&
@@ -2149,5 +2182,5 @@ void cl::ResetAllOptionOccurrences() {
 
 void LLVMParseCommandLineOptions(int argc, const char *const *argv,
                                  const char *Overview) {
-  llvm::cl::ParseCommandLineOptions(argc, argv, Overview, true);
+  llvm::cl::ParseCommandLineOptions(argc, argv, StringRef(Overview), true);
 }