llvm/tools/llvm-lto2/llvm-lto2.cpp

   1 //===-- llvm-lto2: test harness for the resolution-based LTO interface ----===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This program takes in a list of bitcode files, links them and performs
  10 // link-time optimization according to the provided symbol resolutions using the
  11 // resolution-based LTO interface, and outputs one or more object files.
  12 //
  13 // This program is intended to eventually replace llvm-lto which uses the legacy
  14 // LTO interface.
  15 //
  16 //===----------------------------------------------------------------------===//
  17
  18 #include "llvm/Bitcode/BitcodeReader.h"
  19 #include "llvm/CodeGen/CommandFlags.h"
  20 #include "llvm/IR/DiagnosticPrinter.h"
  21 #include "llvm/LTO/LTO.h"
  22 #include "llvm/Passes/PassPlugin.h"
  23 #include "llvm/Remarks/HotnessThresholdParser.h"
  24 #include "llvm/Support/Caching.h"
  25 #include "llvm/Support/CommandLine.h"
  26 #include "llvm/Support/FileSystem.h"
  27 #include "llvm/Support/InitLLVM.h"
  28 #include "llvm/Support/PluginLoader.h"
  29 #include "llvm/Support/TargetSelect.h"
  30 #include "llvm/Support/Threading.h"
  31 #include <atomic>
  32
  33 using namespace llvm;
  34 using namespace lto;
  35
  36 static codegen::RegisterCodeGenFlags CGF;
  37
  38 static cl::opt<char>
  39     OptLevel("O",
  40              cl::desc("Optimization level. [-O0, -O1, -O2, or -O3] "
  41                       "(default = '-O2')"),
  42              cl::Prefix, cl::init('2'));
  43
  44 static cl::opt<char> CGOptLevel(
  45     "cg-opt-level",
  46     cl::desc("Codegen optimization level (0, 1, 2 or 3, default = '2')"),
  47     cl::init('2'));
  48
  49 static cl::list<std::string> InputFilenames(cl::Positional, cl::OneOrMore,
  50                                             cl::desc("<input bitcode files>"));
  51
  52 static cl::opt<std::string> OutputFilename("o", cl::Required,
  53                                            cl::desc("Output filename"),
  54                                            cl::value_desc("filename"));
  55
  56 static cl::opt<std::string> CacheDir("cache-dir", cl::desc("Cache Directory"),
  57                                      cl::value_desc("directory"));
  58
  59 static cl::opt<std::string> OptPipeline("opt-pipeline",
  60                                         cl::desc("Optimizer Pipeline"),
  61                                         cl::value_desc("pipeline"));
  62
  63 static cl::opt<std::string> AAPipeline("aa-pipeline",
  64                                        cl::desc("Alias Analysis Pipeline"),
  65                                        cl::value_desc("aapipeline"));
  66
  67 static cl::opt<bool> SaveTemps("save-temps", cl::desc("Save temporary files"));
  68
  69 static cl::list<std::string> SelectSaveTemps(
  70     "select-save-temps",
  71     cl::value_desc("One, or multiple of: "
  72                    "resolution,preopt,promote,internalize,import,opt,precodegen"
  73                    ",combinedindex"),
  74     cl::desc("Save selected temporary files. Cannot be specified together with "
  75              "-save-temps"),
  76     cl::CommaSeparated);
  77
  78 constexpr const char *SaveTempsValues[] = {
  79     "resolution", "preopt", "promote",    "internalize",
  80     "import",     "opt",    "precodegen", "combinedindex"};
  81
  82 static cl::opt<bool>
  83     ThinLTODistributedIndexes("thinlto-distributed-indexes",
  84                               cl::desc("Write out individual index and "
  85                                        "import files for the "
  86                                        "distributed backend case"));
  87
  88 static cl::opt<bool>
  89     ThinLTOEmitIndexes("thinlto-emit-indexes",
  90                        cl::desc("Write out individual index files via "
  91                                 "InProcessThinLTO"));
  92
  93 static cl::opt<bool>
  94     ThinLTOEmitImports("thinlto-emit-imports",
  95                        cl::desc("Write out individual imports files via "
  96                                 "InProcessThinLTO. Has no effect unless "
  97                                 "specified with -thinlto-emit-indexes or "
  98                                 "-thinlto-distributed-indexes"));
  99
 100 // Default to using all available threads in the system, but using only one
 101 // thread per core (no SMT).
 102 // Use -thinlto-threads=all to use hardware_concurrency() instead, which means
 103 // to use all hardware threads or cores in the system.
 104 static cl::opt<std::string> Threads("thinlto-threads");
 105
 106 static cl::list<std::string> SymbolResolutions(
 107     "r",
 108     cl::desc("Specify a symbol resolution: filename,symbolname,resolution\n"
 109              "where \"resolution\" is a sequence (which may be empty) of the\n"
 110              "following characters:\n"
 111              " p - prevailing: the linker has chosen this definition of the\n"
 112              "     symbol\n"
 113              " l - local: the definition of this symbol is unpreemptable at\n"
 114              "     runtime and is known to be in this linkage unit\n"
 115              " x - externally visible: the definition of this symbol is\n"
 116              "     visible outside of the LTO unit\n"
 117              "A resolution for each symbol must be specified"));
 118
 119 static cl::opt<std::string> OverrideTriple(
 120     "override-triple",
 121     cl::desc("Replace target triples in input files with this triple"));
 122
 123 static cl::opt<std::string> DefaultTriple(
 124     "default-triple",
 125     cl::desc(
 126         "Replace unspecified target triples in input files with this triple"));
 127
 128 static cl::opt<bool> RemarksWithHotness(
 129     "pass-remarks-with-hotness",
 130     cl::desc("With PGO, include profile count in optimization remarks"),
 131     cl::Hidden);
 132
 133 cl::opt<std::optional<uint64_t>, false, remarks::HotnessThresholdParser>
 134     RemarksHotnessThreshold(
 135         "pass-remarks-hotness-threshold",
 136         cl::desc("Minimum profile count required for an "
 137                  "optimization remark to be output."
 138                  " Use 'auto' to apply the threshold from profile summary."),
 139         cl::value_desc("uint or 'auto'"), cl::init(0), cl::Hidden);
 140
 141 static cl::opt<std::string>
 142     RemarksFilename("pass-remarks-output",
 143                     cl::desc("Output filename for pass remarks"),
 144                     cl::value_desc("filename"));
 145
 146 static cl::opt<std::string>
 147     RemarksPasses("pass-remarks-filter",
 148                   cl::desc("Only record optimization remarks from passes whose "
 149                            "names match the given regular expression"),
 150                   cl::value_desc("regex"));
 151
 152 static cl::opt<std::string> RemarksFormat(
 153     "pass-remarks-format",
 154     cl::desc("The format used for serializing remarks (default: YAML)"),
 155     cl::value_desc("format"), cl::init("yaml"));
 156
 157 static cl::opt<std::string>
 158     SamplePGOFile("lto-sample-profile-file",
 159                   cl::desc("Specify a SamplePGO profile file"));
 160
 161 static cl::opt<std::string>
 162     CSPGOFile("lto-cspgo-profile-file",
 163               cl::desc("Specify a context sensitive PGO profile file"));
 164
 165 static cl::opt<bool>
 166     RunCSIRInstr("lto-cspgo-gen",
 167                  cl::desc("Run PGO context sensitive IR instrumentation"),
 168                  cl::Hidden);
 169
 170 static cl::opt<bool>
 171     DebugPassManager("debug-pass-manager", cl::Hidden,
 172                      cl::desc("Print pass management debugging information"));
 173
 174 static cl::opt<std::string>
 175     StatsFile("stats-file", cl::desc("Filename to write statistics to"));
 176
 177 static cl::list<std::string>
 178     PassPlugins("load-pass-plugin",
 179                 cl::desc("Load passes from plugin library"));
 180
 181 static cl::opt<std::string> UnifiedLTOMode("unified-lto", cl::Optional,
 182                                            cl::desc("Set LTO mode"),
 183                                            cl::value_desc("mode"));
 184
 185 static cl::opt<bool> EnableFreestanding(
 186     "lto-freestanding",
 187     cl::desc("Enable Freestanding (disable builtins / TLI) during LTO"),
 188     cl::Hidden);
 189
 190 static cl::opt<bool> TryUseNewDbgInfoFormat(
 191     "try-experimental-debuginfo-iterators",
 192     cl::desc("Enable debuginfo iterator positions, if they're built in"),
 193     cl::init(false), cl::Hidden);
 194
 195 extern cl::opt<bool> UseNewDbgInfoFormat;
 196 extern cl::opt<cl::boolOrDefault> LoadBitcodeIntoNewDbgInfoFormat;
 197 extern cl::opt<cl::boolOrDefault> PreserveInputDbgFormat;
 198
 199 static void check(Error E, std::string Msg) {
 200   if (!E)
 201     return;
 202   handleAllErrors(std::move(E), [&](ErrorInfoBase &EIB) {
 203     errs() << "llvm-lto2: " << Msg << ": " << EIB.message().c_str() << '\n';
 204   });
 205   exit(1);
 206 }
 207
 208 template <typename T> static T check(Expected<T> E, std::string Msg) {
 209   if (E)
 210     return std::move(*E);
 211   check(E.takeError(), Msg);
 212   return T();
 213 }
 214
 215 static void check(std::error_code EC, std::string Msg) {
 216   check(errorCodeToError(EC), Msg);
 217 }
 218
 219 template <typename T> static T check(ErrorOr<T> E, std::string Msg) {
 220   if (E)
 221     return std::move(*E);
 222   check(E.getError(), Msg);
 223   return T();
 224 }
 225
 226 static int usage() {
 227   errs() << "Available subcommands: dump-symtab run\n";
 228   return 1;
 229 }
 230
 231 static int run(int argc, char **argv) {
 232   cl::ParseCommandLineOptions(argc, argv, "Resolution-based LTO test harness");
 233   // Load bitcode into the new debug info format by default.
 234   if (LoadBitcodeIntoNewDbgInfoFormat == cl::boolOrDefault::BOU_UNSET)
 235     LoadBitcodeIntoNewDbgInfoFormat = cl::boolOrDefault::BOU_TRUE;
 236
 237   // RemoveDIs debug-info transition: tests may request that we /try/ to use the
 238   // new debug-info format.
 239   if (TryUseNewDbgInfoFormat) {
 240     // Turn the new debug-info format on.
 241     UseNewDbgInfoFormat = true;
 242   }
 243   // Since llvm-lto2 collects multiple IR modules together, for simplicity's
 244   // sake we disable the "PreserveInputDbgFormat" flag to enforce a single debug
 245   // info format.
 246   PreserveInputDbgFormat = cl::boolOrDefault::BOU_FALSE;
 247
 248   // FIXME: Workaround PR30396 which means that a symbol can appear
 249   // more than once if it is defined in module-level assembly and
 250   // has a GV declaration. We allow (file, symbol) pairs to have multiple
 251   // resolutions and apply them in the order observed.
 252   std::map<std::pair<std::string, std::string>, std::list<SymbolResolution>>
 253       CommandLineResolutions;
 254   for (StringRef R : SymbolResolutions) {
 255     StringRef Rest, FileName, SymbolName;
 256     std::tie(FileName, Rest) = R.split(',');
 257     if (Rest.empty()) {
 258       llvm::errs() << "invalid resolution: " << R << '\n';
 259       return 1;
 260     }
 261     std::tie(SymbolName, Rest) = Rest.split(',');
 262     SymbolResolution Res;
 263     for (char C : Rest) {
 264       if (C == 'p')
 265         Res.Prevailing = true;
 266       else if (C == 'l')
 267         Res.FinalDefinitionInLinkageUnit = true;
 268       else if (C == 'x')
 269         Res.VisibleToRegularObj = true;
 270       else if (C == 'r')
 271         Res.LinkerRedefined = true;
 272       else {
 273         llvm::errs() << "invalid character " << C << " in resolution: " << R
 274                      << '\n';
 275         return 1;
 276       }
 277     }
 278     CommandLineResolutions[{std::string(FileName), std::string(SymbolName)}]
 279         .push_back(Res);
 280   }
 281
 282   std::vector<std::unique_ptr<MemoryBuffer>> MBs;
 283
 284   Config Conf;
 285
 286   Conf.CPU = codegen::getMCPU();
 287   Conf.Options = codegen::InitTargetOptionsFromCodeGenFlags(Triple());
 288   Conf.MAttrs = codegen::getMAttrs();
 289   if (auto RM = codegen::getExplicitRelocModel())
 290     Conf.RelocModel = *RM;
 291   Conf.CodeModel = codegen::getExplicitCodeModel();
 292
 293   Conf.DebugPassManager = DebugPassManager;
 294
 295   if (SaveTemps && !SelectSaveTemps.empty()) {
 296     llvm::errs() << "-save-temps cannot be specified with -select-save-temps\n";
 297     return 1;
 298   }
 299   if (SaveTemps || !SelectSaveTemps.empty()) {
 300     DenseSet<StringRef> SaveTempsArgs;
 301     for (auto &S : SelectSaveTemps)
 302       if (is_contained(SaveTempsValues, S))
 303         SaveTempsArgs.insert(S);
 304       else {
 305         llvm::errs() << ("invalid -select-save-temps argument: " + S) << '\n';
 306         return 1;
 307       }
 308     check(Conf.addSaveTemps(OutputFilename + ".", false, SaveTempsArgs),
 309           "Config::addSaveTemps failed");
 310   }
 311
 312   // Optimization remarks.
 313   Conf.RemarksFilename = RemarksFilename;
 314   Conf.RemarksPasses = RemarksPasses;
 315   Conf.RemarksWithHotness = RemarksWithHotness;
 316   Conf.RemarksHotnessThreshold = RemarksHotnessThreshold;
 317   Conf.RemarksFormat = RemarksFormat;
 318
 319   Conf.SampleProfile = SamplePGOFile;
 320   Conf.CSIRProfile = CSPGOFile;
 321   Conf.RunCSIRInstr = RunCSIRInstr;
 322
 323   // Run a custom pipeline, if asked for.
 324   Conf.OptPipeline = OptPipeline;
 325   Conf.AAPipeline = AAPipeline;
 326
 327   Conf.OptLevel = OptLevel - '0';
 328   Conf.Freestanding = EnableFreestanding;
 329   for (auto &PluginFN : PassPlugins)
 330     Conf.PassPlugins.push_back(PluginFN);
 331   if (auto Level = CodeGenOpt::parseLevel(CGOptLevel)) {
 332     Conf.CGOptLevel = *Level;
 333   } else {
 334     llvm::errs() << "invalid cg optimization level: " << CGOptLevel << '\n';
 335     return 1;
 336   }
 337
 338   if (auto FT = codegen::getExplicitFileType())
 339     Conf.CGFileType = *FT;
 340
 341   Conf.OverrideTriple = OverrideTriple;
 342   Conf.DefaultTriple = DefaultTriple;
 343   Conf.StatsFile = StatsFile;
 344   Conf.PTO.LoopVectorization = Conf.OptLevel > 1;
 345   Conf.PTO.SLPVectorization = Conf.OptLevel > 1;
 346
 347   ThinBackend Backend;
 348   if (ThinLTODistributedIndexes)
 349     Backend = createWriteIndexesThinBackend(llvm::hardware_concurrency(Threads),
 350                                             /*OldPrefix=*/"",
 351                                             /*NewPrefix=*/"",
 352                                             /*NativeObjectPrefix=*/"",
 353                                             ThinLTOEmitImports,
 354                                             /*LinkedObjectsFile=*/nullptr,
 355                                             /*OnWrite=*/{});
 356   else
 357     Backend = createInProcessThinBackend(
 358         llvm::heavyweight_hardware_concurrency(Threads),
 359         /* OnWrite */ {}, ThinLTOEmitIndexes, ThinLTOEmitImports);
 360
 361   // Track whether we hit an error; in particular, in the multi-threaded case,
 362   // we can't exit() early because the rest of the threads wouldn't have had a
 363   // change to be join-ed, and that would result in a "terminate called without
 364   // an active exception". Altogether, this results in nondeterministic
 365   // behavior. Instead, we don't exit in the multi-threaded case, but we make
 366   // sure to report the error and then at the end (after joining cleanly)
 367   // exit(1).
 368   std::atomic<bool> HasErrors;
 369   std::atomic_init(&HasErrors, false);
 370   Conf.DiagHandler = [&](const DiagnosticInfo &DI) {
 371     DiagnosticPrinterRawOStream DP(errs());
 372     DI.print(DP);
 373     errs() << '\n';
 374     if (DI.getSeverity() == DS_Error)
 375       HasErrors = true;
 376   };
 377
 378   LTO::LTOKind LTOMode = LTO::LTOK_Default;
 379
 380   if (UnifiedLTOMode == "full") {
 381     LTOMode = LTO::LTOK_UnifiedRegular;
 382   } else if (UnifiedLTOMode == "thin") {
 383     LTOMode = LTO::LTOK_UnifiedThin;
 384   } else if (UnifiedLTOMode == "default") {
 385     LTOMode = LTO::LTOK_Default;
 386   } else if (!UnifiedLTOMode.empty()) {
 387     llvm::errs() << "invalid LTO mode\n";
 388     return 1;
 389   }
 390
 391   LTO Lto(std::move(Conf), std::move(Backend), 1, LTOMode);
 392
 393   for (std::string F : InputFilenames) {
 394     std::unique_ptr<MemoryBuffer> MB = check(MemoryBuffer::getFile(F), F);
 395     std::unique_ptr<InputFile> Input =
 396         check(InputFile::create(MB->getMemBufferRef()), F);
 397
 398     std::vector<SymbolResolution> Res;
 399     for (const InputFile::Symbol &Sym : Input->symbols()) {
 400       auto I = CommandLineResolutions.find({F, std::string(Sym.getName())});
 401       // If it isn't found, look for ".", which would have been added
 402       // (followed by a hash) when the symbol was promoted during module
 403       // splitting if it was defined in one part and used in the other.
 404       // Try looking up the symbol name before the suffix.
 405       if (I == CommandLineResolutions.end()) {
 406         auto SplitName = Sym.getName().rsplit(".");
 407         I = CommandLineResolutions.find({F, std::string(SplitName.first)});
 408       }
 409       if (I == CommandLineResolutions.end()) {
 410         llvm::errs() << argv[0] << ": missing symbol resolution for " << F
 411                      << ',' << Sym.getName() << '\n';
 412         HasErrors = true;
 413       } else {
 414         Res.push_back(I->second.front());
 415         I->second.pop_front();
 416         if (I->second.empty())
 417           CommandLineResolutions.erase(I);
 418       }
 419     }
 420
 421     if (HasErrors)
 422       continue;
 423
 424     MBs.push_back(std::move(MB));
 425     check(Lto.add(std::move(Input), Res), F);
 426   }
 427
 428   if (!CommandLineResolutions.empty()) {
 429     HasErrors = true;
 430     for (auto UnusedRes : CommandLineResolutions)
 431       llvm::errs() << argv[0] << ": unused symbol resolution for "
 432                    << UnusedRes.first.first << ',' << UnusedRes.first.second
 433                    << '\n';
 434   }
 435   if (HasErrors)
 436     return 1;
 437
 438   auto AddStream =
 439       [&](size_t Task,
 440           const Twine &ModuleName) -> std::unique_ptr<CachedFileStream> {
 441     std::string Path = OutputFilename + "." + utostr(Task);
 442
 443     std::error_code EC;
 444     auto S = std::make_unique<raw_fd_ostream>(Path, EC, sys::fs::OF_None);
 445     check(EC, Path);
 446     return std::make_unique<CachedFileStream>(std::move(S), Path);
 447   };
 448
 449   auto AddBuffer = [&](size_t Task, const Twine &ModuleName,
 450                        std::unique_ptr<MemoryBuffer> MB) {
 451     *AddStream(Task, ModuleName)->OS << MB->getBuffer();
 452   };
 453
 454   FileCache Cache;
 455   if (!CacheDir.empty())
 456     Cache = check(localCache("ThinLTO", "Thin", CacheDir, AddBuffer),
 457                   "failed to create cache");
 458
 459   check(Lto.run(AddStream, Cache), "LTO::run failed");
 460   return static_cast<int>(HasErrors);
 461 }
 462
 463 static int dumpSymtab(int argc, char **argv) {
 464   for (StringRef F : make_range(argv + 1, argv + argc)) {
 465     std::unique_ptr<MemoryBuffer> MB =
 466         check(MemoryBuffer::getFile(F), std::string(F));
 467     BitcodeFileContents BFC =
 468         check(getBitcodeFileContents(*MB), std::string(F));
 469
 470     if (BFC.Symtab.size() >= sizeof(irsymtab::storage::Header)) {
 471       auto *Hdr = reinterpret_cast<const irsymtab::storage::Header *>(
 472           BFC.Symtab.data());
 473       outs() << "version: " << Hdr->Version << '\n';
 474       if (Hdr->Version == irsymtab::storage::Header::kCurrentVersion)
 475         outs() << "producer: " << Hdr->Producer.get(BFC.StrtabForSymtab)
 476                << '\n';
 477     }
 478
 479     std::unique_ptr<InputFile> Input =
 480         check(InputFile::create(MB->getMemBufferRef()), std::string(F));
 481
 482     outs() << "target triple: " << Input->getTargetTriple() << '\n';
 483     Triple TT(Input->getTargetTriple());
 484
 485     outs() << "source filename: " << Input->getSourceFileName() << '\n';
 486
 487     if (TT.isOSBinFormatCOFF())
 488       outs() << "linker opts: " << Input->getCOFFLinkerOpts() << '\n';
 489
 490     if (TT.isOSBinFormatELF()) {
 491       outs() << "dependent libraries:";
 492       for (auto L : Input->getDependentLibraries())
 493         outs() << " \"" << L << "\"";
 494       outs() << '\n';
 495     }
 496
 497     ArrayRef<std::pair<StringRef, Comdat::SelectionKind>> ComdatTable =
 498         Input->getComdatTable();
 499     for (const InputFile::Symbol &Sym : Input->symbols()) {
 500       switch (Sym.getVisibility()) {
 501       case GlobalValue::HiddenVisibility:
 502         outs() << 'H';
 503         break;
 504       case GlobalValue::ProtectedVisibility:
 505         outs() << 'P';
 506         break;
 507       case GlobalValue::DefaultVisibility:
 508         outs() << 'D';
 509         break;
 510       }
 511
 512       auto PrintBool = [&](char C, bool B) { outs() << (B ? C : '-'); };
 513       PrintBool('U', Sym.isUndefined());
 514       PrintBool('C', Sym.isCommon());
 515       PrintBool('W', Sym.isWeak());
 516       PrintBool('I', Sym.isIndirect());
 517       PrintBool('O', Sym.canBeOmittedFromSymbolTable());
 518       PrintBool('T', Sym.isTLS());
 519       PrintBool('X', Sym.isExecutable());
 520       outs() << ' ' << Sym.getName() << '\n';
 521
 522       if (Sym.isCommon())
 523         outs() << "         size " << Sym.getCommonSize() << " align "
 524                << Sym.getCommonAlignment() << '\n';
 525
 526       int Comdat = Sym.getComdatIndex();
 527       if (Comdat != -1) {
 528         outs() << "         comdat ";
 529         switch (ComdatTable[Comdat].second) {
 530         case Comdat::Any:
 531           outs() << "any";
 532           break;
 533         case Comdat::ExactMatch:
 534           outs() << "exactmatch";
 535           break;
 536         case Comdat::Largest:
 537           outs() << "largest";
 538           break;
 539         case Comdat::NoDeduplicate:
 540           outs() << "nodeduplicate";
 541           break;
 542         case Comdat::SameSize:
 543           outs() << "samesize";
 544           break;
 545         }
 546         outs() << ' ' << ComdatTable[Comdat].first << '\n';
 547       }
 548
 549       if (TT.isOSBinFormatCOFF() && Sym.isWeak() && Sym.isIndirect())
 550         outs() << "         fallback " << Sym.getCOFFWeakExternalFallback() << '\n';
 551
 552       if (!Sym.getSectionName().empty())
 553         outs() << "         section " << Sym.getSectionName() << "\n";
 554     }
 555
 556     outs() << '\n';
 557   }
 558
 559   return 0;
 560 }
 561
 562 int main(int argc, char **argv) {
 563   InitLLVM X(argc, argv);
 564   InitializeAllTargets();
 565   InitializeAllTargetMCs();
 566   InitializeAllAsmPrinters();
 567   InitializeAllAsmParsers();
 568
 569   // FIXME: This should use llvm::cl subcommands, but it isn't currently
 570   // possible to pass an argument not associated with a subcommand to a
 571   // subcommand (e.g. -use-new-pm).
 572   if (argc < 2)
 573     return usage();
 574
 575   StringRef Subcommand = argv[1];
 576   // Ensure that argv[0] is correct after adjusting argv/argc.
 577   argv[1] = argv[0];
 578   if (Subcommand == "dump-symtab")
 579     return dumpSymtab(argc - 1, argv + 1);
 580   if (Subcommand == "run")
 581     return run(argc - 1, argv + 1);
 582   return usage();
 583 }