tools/llc/llc.cpp

   1 //===-- llc.cpp - Implement the LLVM Native Code Generator ----------------===//
   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 is the llc code generator driver. It provides a convenient
  10 // command-line interface for generating native assembly-language code
  11 // or C code, given LLVM bitcode.
  12 //
  13 //===----------------------------------------------------------------------===//
  14
  15 #include "llvm/ADT/STLExtras.h"
  16 #include "llvm/ADT/Triple.h"
  17 #include "llvm/Analysis/TargetLibraryInfo.h"
  18 #include "llvm/CodeGen/CommandFlags.inc"
  19 #include "llvm/CodeGen/LinkAllAsmWriterComponents.h"
  20 #include "llvm/CodeGen/LinkAllCodegenComponents.h"
  21 #include "llvm/CodeGen/MIRParser/MIRParser.h"
  22 #include "llvm/CodeGen/MachineFunctionPass.h"
  23 #include "llvm/CodeGen/MachineModuleInfo.h"
  24 #include "llvm/CodeGen/TargetPassConfig.h"
  25 #include "llvm/CodeGen/TargetSubtargetInfo.h"
  26 #include "llvm/IR/AutoUpgrade.h"
  27 #include "llvm/IR/DataLayout.h"
  28 #include "llvm/IR/DiagnosticInfo.h"
  29 #include "llvm/IR/DiagnosticPrinter.h"
  30 #include "llvm/IR/IRPrintingPasses.h"
  31 #include "llvm/IR/LLVMContext.h"
  32 #include "llvm/IR/LegacyPassManager.h"
  33 #include "llvm/IR/Module.h"
  34 #include "llvm/IR/Verifier.h"
  35 #include "llvm/IRReader/IRReader.h"
  36 #include "llvm/MC/SubtargetFeature.h"
  37 #include "llvm/Pass.h"
  38 #include "llvm/Support/CommandLine.h"
  39 #include "llvm/Support/Debug.h"
  40 #include "llvm/Support/FileSystem.h"
  41 #include "llvm/Support/FormattedStream.h"
  42 #include "llvm/Support/Host.h"
  43 #include "llvm/Support/InitLLVM.h"
  44 #include "llvm/Support/ManagedStatic.h"
  45 #include "llvm/Support/PluginLoader.h"
  46 #include "llvm/Support/SourceMgr.h"
  47 #include "llvm/Support/TargetRegistry.h"
  48 #include "llvm/Support/TargetSelect.h"
  49 #include "llvm/Support/ToolOutputFile.h"
  50 #include "llvm/Support/WithColor.h"
  51 #include "llvm/Target/TargetMachine.h"
  52 #include "llvm/Transforms/Utils/Cloning.h"
  53 #include <memory>
  54 using namespace llvm;
  55
  56 // General options for llc.  Other pass-specific options are specified
  57 // within the corresponding llc passes, and target-specific options
  58 // and back-end code generation options are specified with the target machine.
  59 //
  60 static cl::opt<std::string>
  61 InputFilename(cl::Positional, cl::desc("<input bitcode>"), cl::init("-"));
  62
  63 static cl::opt<std::string>
  64 InputLanguage("x", cl::desc("Input language ('ir' or 'mir')"));
  65
  66 static cl::opt<std::string>
  67 OutputFilename("o", cl::desc("Output filename"), cl::value_desc("filename"));
  68
  69 static cl::opt<std::string>
  70     SplitDwarfOutputFile("split-dwarf-output",
  71                          cl::desc(".dwo output filename"),
  72                          cl::value_desc("filename"));
  73
  74 static cl::opt<unsigned>
  75 TimeCompilations("time-compilations", cl::Hidden, cl::init(1u),
  76                  cl::value_desc("N"),
  77                  cl::desc("Repeat compilation N times for timing"));
  78
  79 static cl::opt<bool>
  80 NoIntegratedAssembler("no-integrated-as", cl::Hidden,
  81                       cl::desc("Disable integrated assembler"));
  82
  83 static cl::opt<bool>
  84     PreserveComments("preserve-as-comments", cl::Hidden,
  85                      cl::desc("Preserve Comments in outputted assembly"),
  86                      cl::init(true));
  87
  88 // Determine optimization level.
  89 static cl::opt<char>
  90 OptLevel("O",
  91          cl::desc("Optimization level. [-O0, -O1, -O2, or -O3] "
  92                   "(default = '-O2')"),
  93          cl::Prefix,
  94          cl::ZeroOrMore,
  95          cl::init(' '));
  96
  97 static cl::opt<std::string>
  98 TargetTriple("mtriple", cl::desc("Override target triple for module"));
  99
 100 static cl::opt<std::string> SplitDwarfFile(
 101     "split-dwarf-file",
 102     cl::desc(
 103         "Specify the name of the .dwo file to encode in the DWARF output"));
 104
 105 static cl::opt<bool> NoVerify("disable-verify", cl::Hidden,
 106                               cl::desc("Do not verify input module"));
 107
 108 static cl::opt<bool> DisableSimplifyLibCalls("disable-simplify-libcalls",
 109                                              cl::desc("Disable simplify-libcalls"));
 110
 111 static cl::opt<bool> ShowMCEncoding("show-mc-encoding", cl::Hidden,
 112                                     cl::desc("Show encoding in .s output"));
 113
 114 static cl::opt<bool> EnableDwarfDirectory(
 115     "enable-dwarf-directory", cl::Hidden,
 116     cl::desc("Use .file directives with an explicit directory."));
 117
 118 static cl::opt<bool> AsmVerbose("asm-verbose",
 119                                 cl::desc("Add comments to directives."),
 120                                 cl::init(true));
 121
 122 static cl::opt<bool>
 123     CompileTwice("compile-twice", cl::Hidden,
 124                  cl::desc("Run everything twice, re-using the same pass "
 125                           "manager and verify the result is the same."),
 126                  cl::init(false));
 127
 128 static cl::opt<bool> DiscardValueNames(
 129     "discard-value-names",
 130     cl::desc("Discard names from Value (other than GlobalValue)."),
 131     cl::init(false), cl::Hidden);
 132
 133 static cl::list<std::string> IncludeDirs("I", cl::desc("include search path"));
 134
 135 static cl::opt<bool> PassRemarksWithHotness(
 136     "pass-remarks-with-hotness",
 137     cl::desc("With PGO, include profile count in optimization remarks"),
 138     cl::Hidden);
 139
 140 static cl::opt<unsigned> PassRemarksHotnessThreshold(
 141     "pass-remarks-hotness-threshold",
 142     cl::desc("Minimum profile count required for an optimization remark to be output"),
 143     cl::Hidden);
 144
 145 static cl::opt<std::string>
 146     RemarksFilename("pass-remarks-output",
 147                     cl::desc("YAML output filename for pass remarks"),
 148                     cl::value_desc("filename"));
 149
 150 namespace {
 151 static ManagedStatic<std::vector<std::string>> RunPassNames;
 152
 153 struct RunPassOption {
 154   void operator=(const std::string &Val) const {
 155     if (Val.empty())
 156       return;
 157     SmallVector<StringRef, 8> PassNames;
 158     StringRef(Val).split(PassNames, ',', -1, false);
 159     for (auto PassName : PassNames)
 160       RunPassNames->push_back(PassName);
 161   }
 162 };
 163 }
 164
 165 static RunPassOption RunPassOpt;
 166
 167 static cl::opt<RunPassOption, true, cl::parser<std::string>> RunPass(
 168     "run-pass",
 169     cl::desc("Run compiler only for specified passes (comma separated list)"),
 170     cl::value_desc("pass-name"), cl::ZeroOrMore, cl::location(RunPassOpt));
 171
 172 static int compileModule(char **, LLVMContext &);
 173
 174 static std::unique_ptr<ToolOutputFile> GetOutputStream(const char *TargetName,
 175                                                        Triple::OSType OS,
 176                                                        const char *ProgName) {
 177   // If we don't yet have an output filename, make one.
 178   if (OutputFilename.empty()) {
 179     if (InputFilename == "-")
 180       OutputFilename = "-";
 181     else {
 182       // If InputFilename ends in .bc or .ll, remove it.
 183       StringRef IFN = InputFilename;
 184       if (IFN.endswith(".bc") || IFN.endswith(".ll"))
 185         OutputFilename = IFN.drop_back(3);
 186       else if (IFN.endswith(".mir"))
 187         OutputFilename = IFN.drop_back(4);
 188       else
 189         OutputFilename = IFN;
 190
 191       switch (FileType) {
 192       case TargetMachine::CGFT_AssemblyFile:
 193         if (TargetName[0] == 'c') {
 194           if (TargetName[1] == 0)
 195             OutputFilename += ".cbe.c";
 196           else if (TargetName[1] == 'p' && TargetName[2] == 'p')
 197             OutputFilename += ".cpp";
 198           else
 199             OutputFilename += ".s";
 200         } else
 201           OutputFilename += ".s";
 202         break;
 203       case TargetMachine::CGFT_ObjectFile:
 204         if (OS == Triple::Win32)
 205           OutputFilename += ".obj";
 206         else
 207           OutputFilename += ".o";
 208         break;
 209       case TargetMachine::CGFT_Null:
 210         OutputFilename += ".null";
 211         break;
 212       }
 213     }
 214   }
 215
 216   // Decide if we need "binary" output.
 217   bool Binary = false;
 218   switch (FileType) {
 219   case TargetMachine::CGFT_AssemblyFile:
 220     break;
 221   case TargetMachine::CGFT_ObjectFile:
 222   case TargetMachine::CGFT_Null:
 223     Binary = true;
 224     break;
 225   }
 226
 227   // Open the file.
 228   std::error_code EC;
 229   sys::fs::OpenFlags OpenFlags = sys::fs::F_None;
 230   if (!Binary)
 231     OpenFlags |= sys::fs::F_Text;
 232   auto FDOut = llvm::make_unique<ToolOutputFile>(OutputFilename, EC, OpenFlags);
 233   if (EC) {
 234     WithColor::error() << EC.message() << '\n';
 235     return nullptr;
 236   }
 237
 238   return FDOut;
 239 }
 240
 241 struct LLCDiagnosticHandler : public DiagnosticHandler {
 242   bool *HasError;
 243   LLCDiagnosticHandler(bool *HasErrorPtr) : HasError(HasErrorPtr) {}
 244   bool handleDiagnostics(const DiagnosticInfo &DI) override {
 245     if (DI.getSeverity() == DS_Error)
 246       *HasError = true;
 247
 248     if (auto *Remark = dyn_cast<DiagnosticInfoOptimizationBase>(&DI))
 249       if (!Remark->isEnabled())
 250         return true;
 251
 252     DiagnosticPrinterRawOStream DP(errs());
 253     errs() << LLVMContext::getDiagnosticMessagePrefix(DI.getSeverity()) << ": ";
 254     DI.print(DP);
 255     errs() << "\n";
 256     return true;
 257   }
 258 };
 259
 260 static void InlineAsmDiagHandler(const SMDiagnostic &SMD, void *Context,
 261                                  unsigned LocCookie) {
 262   bool *HasError = static_cast<bool *>(Context);
 263   if (SMD.getKind() == SourceMgr::DK_Error)
 264     *HasError = true;
 265
 266   SMD.print(nullptr, errs());
 267
 268   // For testing purposes, we print the LocCookie here.
 269   if (LocCookie)
 270     WithColor::note() << "!srcloc = " << LocCookie << "\n";
 271 }
 272
 273 // main - Entry point for the llc compiler.
 274 //
 275 int main(int argc, char **argv) {
 276   InitLLVM X(argc, argv);
 277
 278   // Enable debug stream buffering.
 279   EnableDebugBuffering = true;
 280
 281   LLVMContext Context;
 282
 283   // Initialize targets first, so that --version shows registered targets.
 284   InitializeAllTargets();
 285   InitializeAllTargetMCs();
 286   InitializeAllAsmPrinters();
 287   InitializeAllAsmParsers();
 288
 289   // Initialize codegen and IR passes used by llc so that the -print-after,
 290   // -print-before, and -stop-after options work.
 291   PassRegistry *Registry = PassRegistry::getPassRegistry();
 292   initializeCore(*Registry);
 293   initializeCodeGen(*Registry);
 294   initializeLoopStrengthReducePass(*Registry);
 295   initializeLowerIntrinsicsPass(*Registry);
 296   initializeEntryExitInstrumenterPass(*Registry);
 297   initializePostInlineEntryExitInstrumenterPass(*Registry);
 298   initializeUnreachableBlockElimLegacyPassPass(*Registry);
 299   initializeConstantHoistingLegacyPassPass(*Registry);
 300   initializeScalarOpts(*Registry);
 301   initializeVectorization(*Registry);
 302   initializeScalarizeMaskedMemIntrinPass(*Registry);
 303   initializeExpandReductionsPass(*Registry);
 304
 305   // Initialize debugging passes.
 306   initializeScavengerTestPass(*Registry);
 307
 308   // Register the target printer for --version.
 309   cl::AddExtraVersionPrinter(TargetRegistry::printRegisteredTargetsForVersion);
 310
 311   cl::ParseCommandLineOptions(argc, argv, "llvm system compiler\n");
 312
 313   Context.setDiscardValueNames(DiscardValueNames);
 314
 315   // Set a diagnostic handler that doesn't exit on the first error
 316   bool HasError = false;
 317   Context.setDiagnosticHandler(
 318       llvm::make_unique<LLCDiagnosticHandler>(&HasError));
 319   Context.setInlineAsmDiagnosticHandler(InlineAsmDiagHandler, &HasError);
 320
 321   if (PassRemarksWithHotness)
 322     Context.setDiagnosticsHotnessRequested(true);
 323
 324   if (PassRemarksHotnessThreshold)
 325     Context.setDiagnosticsHotnessThreshold(PassRemarksHotnessThreshold);
 326
 327   std::unique_ptr<ToolOutputFile> YamlFile;
 328   if (RemarksFilename != "") {
 329     std::error_code EC;
 330     YamlFile =
 331         llvm::make_unique<ToolOutputFile>(RemarksFilename, EC, sys::fs::F_None);
 332     if (EC) {
 333       WithColor::error(errs(), argv[0]) << EC.message() << '\n';
 334       return 1;
 335     }
 336     Context.setDiagnosticsOutputFile(
 337         llvm::make_unique<yaml::Output>(YamlFile->os()));
 338   }
 339
 340   if (InputLanguage != "" && InputLanguage != "ir" &&
 341       InputLanguage != "mir") {
 342     WithColor::error(errs(), argv[0])
 343         << "input language must be '', 'IR' or 'MIR'\n";
 344     return 1;
 345   }
 346
 347   // Compile the module TimeCompilations times to give better compile time
 348   // metrics.
 349   for (unsigned I = TimeCompilations; I; --I)
 350     if (int RetVal = compileModule(argv, Context))
 351       return RetVal;
 352
 353   if (YamlFile)
 354     YamlFile->keep();
 355   return 0;
 356 }
 357
 358 static bool addPass(PassManagerBase &PM, const char *argv0,
 359                     StringRef PassName, TargetPassConfig &TPC) {
 360   if (PassName == "none")
 361     return false;
 362
 363   const PassRegistry *PR = PassRegistry::getPassRegistry();
 364   const PassInfo *PI = PR->getPassInfo(PassName);
 365   if (!PI) {
 366     WithColor::error(errs(), argv0)
 367         << "run-pass " << PassName << " is not registered.\n";
 368     return true;
 369   }
 370
 371   Pass *P;
 372   if (PI->getNormalCtor())
 373     P = PI->getNormalCtor()();
 374   else {
 375     WithColor::error(errs(), argv0)
 376         << "cannot create pass: " << PI->getPassName() << "\n";
 377     return true;
 378   }
 379   std::string Banner = std::string("After ") + std::string(P->getPassName());
 380   PM.add(P);
 381   TPC.printAndVerify(Banner);
 382
 383   return false;
 384 }
 385
 386 static int compileModule(char **argv, LLVMContext &Context) {
 387   // Load the module to be compiled...
 388   SMDiagnostic Err;
 389   std::unique_ptr<Module> M;
 390   std::unique_ptr<MIRParser> MIR;
 391   Triple TheTriple;
 392
 393   bool SkipModule = MCPU == "help" ||
 394                     (!MAttrs.empty() && MAttrs.front() == "help");
 395
 396   // If user just wants to list available options, skip module loading
 397   if (!SkipModule) {
 398     if (InputLanguage == "mir" ||
 399         (InputLanguage == "" && StringRef(InputFilename).endswith(".mir"))) {
 400       MIR = createMIRParserFromFile(InputFilename, Err, Context);
 401       if (MIR)
 402         M = MIR->parseIRModule();
 403     } else
 404       M = parseIRFile(InputFilename, Err, Context, false);
 405     if (!M) {
 406       Err.print(argv[0], WithColor::error(errs(), argv[0]));
 407       return 1;
 408     }
 409
 410     // If we are supposed to override the target triple, do so now.
 411     if (!TargetTriple.empty())
 412       M->setTargetTriple(Triple::normalize(TargetTriple));
 413     TheTriple = Triple(M->getTargetTriple());
 414   } else {
 415     TheTriple = Triple(Triple::normalize(TargetTriple));
 416   }
 417
 418   if (TheTriple.getTriple().empty())
 419     TheTriple.setTriple(sys::getDefaultTargetTriple());
 420
 421   // Get the target specific parser.
 422   std::string Error;
 423   const Target *TheTarget = TargetRegistry::lookupTarget(MArch, TheTriple,
 424                                                          Error);
 425   if (!TheTarget) {
 426     WithColor::error(errs(), argv[0]) << Error;
 427     return 1;
 428   }
 429
 430   std::string CPUStr = getCPUStr(), FeaturesStr = getFeaturesStr();
 431
 432   CodeGenOpt::Level OLvl = CodeGenOpt::Default;
 433   switch (OptLevel) {
 434   default:
 435     WithColor::error(errs(), argv[0]) << "invalid optimization level.\n";
 436     return 1;
 437   case ' ': break;
 438   case '0': OLvl = CodeGenOpt::None; break;
 439   case '1': OLvl = CodeGenOpt::Less; break;
 440   case '2': OLvl = CodeGenOpt::Default; break;
 441   case '3': OLvl = CodeGenOpt::Aggressive; break;
 442   }
 443
 444   TargetOptions Options = InitTargetOptionsFromCodeGenFlags();
 445   Options.DisableIntegratedAS = NoIntegratedAssembler;
 446   Options.MCOptions.ShowMCEncoding = ShowMCEncoding;
 447   Options.MCOptions.MCUseDwarfDirectory = EnableDwarfDirectory;
 448   Options.MCOptions.AsmVerbose = AsmVerbose;
 449   Options.MCOptions.PreserveAsmComments = PreserveComments;
 450   Options.MCOptions.IASSearchPaths = IncludeDirs;
 451   Options.MCOptions.SplitDwarfFile = SplitDwarfFile;
 452
 453   std::unique_ptr<TargetMachine> Target(TheTarget->createTargetMachine(
 454       TheTriple.getTriple(), CPUStr, FeaturesStr, Options, getRelocModel(),
 455       getCodeModel(), OLvl));
 456
 457   assert(Target && "Could not allocate target machine!");
 458
 459   // If we don't have a module then just exit now. We do this down
 460   // here since the CPU/Feature help is underneath the target machine
 461   // creation.
 462   if (SkipModule)
 463     return 0;
 464
 465   assert(M && "Should have exited if we didn't have a module!");
 466   if (FloatABIForCalls != FloatABI::Default)
 467     Options.FloatABIType = FloatABIForCalls;
 468
 469   // Figure out where we are going to send the output.
 470   std::unique_ptr<ToolOutputFile> Out =
 471       GetOutputStream(TheTarget->getName(), TheTriple.getOS(), argv[0]);
 472   if (!Out) return 1;
 473
 474   std::unique_ptr<ToolOutputFile> DwoOut;
 475   if (!SplitDwarfOutputFile.empty()) {
 476     std::error_code EC;
 477     DwoOut = llvm::make_unique<ToolOutputFile>(SplitDwarfOutputFile, EC,
 478                                                sys::fs::F_None);
 479     if (EC) {
 480       WithColor::error(errs(), argv[0]) << EC.message() << '\n';
 481       return 1;
 482     }
 483   }
 484
 485   // Build up all of the passes that we want to do to the module.
 486   legacy::PassManager PM;
 487
 488   // Add an appropriate TargetLibraryInfo pass for the module's triple.
 489   TargetLibraryInfoImpl TLII(Triple(M->getTargetTriple()));
 490
 491   // The -disable-simplify-libcalls flag actually disables all builtin optzns.
 492   if (DisableSimplifyLibCalls)
 493     TLII.disableAllFunctions();
 494   PM.add(new TargetLibraryInfoWrapperPass(TLII));
 495
 496   // Add the target data from the target machine, if it exists, or the module.
 497   M->setDataLayout(Target->createDataLayout());
 498
 499   // This needs to be done after setting datalayout since it calls verifier
 500   // to check debug info whereas verifier relies on correct datalayout.
 501   UpgradeDebugInfo(*M);
 502
 503   // Verify module immediately to catch problems before doInitialization() is
 504   // called on any passes.
 505   if (!NoVerify && verifyModule(*M, &errs())) {
 506     std::string Prefix =
 507         (Twine(argv[0]) + Twine(": ") + Twine(InputFilename)).str();
 508     WithColor::error(errs(), Prefix) << "input module is broken!\n";
 509     return 1;
 510   }
 511
 512   // Override function attributes based on CPUStr, FeaturesStr, and command line
 513   // flags.
 514   setFunctionAttributes(CPUStr, FeaturesStr, *M);
 515
 516   if (RelaxAll.getNumOccurrences() > 0 &&
 517       FileType != TargetMachine::CGFT_ObjectFile)
 518     WithColor::warning(errs(), argv[0])
 519         << ": warning: ignoring -mc-relax-all because filetype != obj";
 520
 521   {
 522     raw_pwrite_stream *OS = &Out->os();
 523
 524     // Manually do the buffering rather than using buffer_ostream,
 525     // so we can memcmp the contents in CompileTwice mode
 526     SmallVector<char, 0> Buffer;
 527     std::unique_ptr<raw_svector_ostream> BOS;
 528     if ((FileType != TargetMachine::CGFT_AssemblyFile &&
 529          !Out->os().supportsSeeking()) ||
 530         CompileTwice) {
 531       BOS = make_unique<raw_svector_ostream>(Buffer);
 532       OS = BOS.get();
 533     }
 534
 535     const char *argv0 = argv[0];
 536     LLVMTargetMachine &LLVMTM = static_cast<LLVMTargetMachine&>(*Target);
 537     MachineModuleInfo *MMI = new MachineModuleInfo(&LLVMTM);
 538
 539     // Construct a custom pass pipeline that starts after instruction
 540     // selection.
 541     if (!RunPassNames->empty()) {
 542       if (!MIR) {
 543         WithColor::warning(errs(), argv[0])
 544             << "run-pass is for .mir file only.\n";
 545         return 1;
 546       }
 547       TargetPassConfig &TPC = *LLVMTM.createPassConfig(PM);
 548       if (TPC.hasLimitedCodeGenPipeline()) {
 549         WithColor::warning(errs(), argv[0])
 550             << "run-pass cannot be used with "
 551             << TPC.getLimitedCodeGenPipelineReason(" and ") << ".\n";
 552         return 1;
 553       }
 554
 555       TPC.setDisableVerify(NoVerify);
 556       PM.add(&TPC);
 557       PM.add(MMI);
 558       TPC.printAndVerify("");
 559       for (const std::string &RunPassName : *RunPassNames) {
 560         if (addPass(PM, argv0, RunPassName, TPC))
 561           return 1;
 562       }
 563       TPC.setInitialized();
 564       PM.add(createPrintMIRPass(*OS));
 565       PM.add(createFreeMachineFunctionPass());
 566     } else if (Target->addPassesToEmitFile(PM, *OS,
 567                                            DwoOut ? &DwoOut->os() : nullptr,
 568                                            FileType, NoVerify, MMI)) {
 569       WithColor::warning(errs(), argv[0])
 570           << "target does not support generation of this"
 571           << " file type!\n";
 572       return 1;
 573     }
 574
 575     if (MIR) {
 576       assert(MMI && "Forgot to create MMI?");
 577       if (MIR->parseMachineFunctions(*M, *MMI))
 578         return 1;
 579     }
 580
 581     // Before executing passes, print the final values of the LLVM options.
 582     cl::PrintOptionValues();
 583
 584     // If requested, run the pass manager over the same module again,
 585     // to catch any bugs due to persistent state in the passes. Note that
 586     // opt has the same functionality, so it may be worth abstracting this out
 587     // in the future.
 588     SmallVector<char, 0> CompileTwiceBuffer;
 589     if (CompileTwice) {
 590       std::unique_ptr<Module> M2(llvm::CloneModule(*M));
 591       PM.run(*M2);
 592       CompileTwiceBuffer = Buffer;
 593       Buffer.clear();
 594     }
 595
 596     PM.run(*M);
 597
 598     auto HasError =
 599         ((const LLCDiagnosticHandler *)(Context.getDiagHandlerPtr()))->HasError;
 600     if (*HasError)
 601       return 1;
 602
 603     // Compare the two outputs and make sure they're the same
 604     if (CompileTwice) {
 605       if (Buffer.size() != CompileTwiceBuffer.size() ||
 606           (memcmp(Buffer.data(), CompileTwiceBuffer.data(), Buffer.size()) !=
 607            0)) {
 608         errs()
 609             << "Running the pass manager twice changed the output.\n"
 610                "Writing the result of the second run to the specified output\n"
 611                "To generate the one-run comparison binary, just run without\n"
 612                "the compile-twice option\n";
 613         Out->os() << Buffer;
 614         Out->keep();
 615         return 1;
 616       }
 617     }
 618
 619     if (BOS) {
 620       Out->os() << Buffer;
 621     }
 622   }
 623
 624   // Declare success.
 625   Out->keep();
 626   if (DwoOut)
 627     DwoOut->keep();
 628
 629   return 0;
 630 }