//.........这里部分代码省略.........

  // Set frame pointer elimination mode.
  if (!CodeGenOpts.DisableFPElim) {
    Options.NoFramePointerElim = false;
    Options.NoFramePointerElimNonLeaf = false;
  } else if (CodeGenOpts.OmitLeafFramePointer) {
    Options.NoFramePointerElim = false;
    Options.NoFramePointerElimNonLeaf = true;
  } else {
    Options.NoFramePointerElim = true;
    Options.NoFramePointerElimNonLeaf = true;
  }

  if (CodeGenOpts.UseInitArray)
    Options.UseInitArray = true;

  // Set float ABI type.
  if (CodeGenOpts.FloatABI == "soft" || CodeGenOpts.FloatABI == "softfp")
    Options.FloatABIType = llvm::FloatABI::Soft;
  else if (CodeGenOpts.FloatABI == "hard")
    Options.FloatABIType = llvm::FloatABI::Hard;
  else {
    assert(CodeGenOpts.FloatABI.empty() && "Invalid float abi!");
    Options.FloatABIType = llvm::FloatABI::Default;
  }

  // Set FP fusion mode.
  switch (LangOpts.getFPContractMode()) {
  case LangOptions::FPC_Off:
    Options.AllowFPOpFusion = llvm::FPOpFusion::Strict;
    break;
  case LangOptions::FPC_On:
    Options.AllowFPOpFusion = llvm::FPOpFusion::Standard;
    break;
  case LangOptions::FPC_Fast:
    Options.AllowFPOpFusion = llvm::FPOpFusion::Fast;
    break;              
  }

  Options.LessPreciseFPMADOption = CodeGenOpts.LessPreciseFPMAD;
  Options.NoInfsFPMath = CodeGenOpts.NoInfsFPMath;
  Options.NoNaNsFPMath = CodeGenOpts.NoNaNsFPMath;
  Options.NoZerosInBSS = CodeGenOpts.NoZeroInitializedInBSS;
  Options.UnsafeFPMath = CodeGenOpts.UnsafeFPMath;
  Options.UseSoftFloat = CodeGenOpts.SoftFloat;
  Options.StackAlignmentOverride = CodeGenOpts.StackAlignment;
  Options.RealignStack = CodeGenOpts.StackRealignment;
  Options.DisableTailCalls = CodeGenOpts.DisableTailCalls;
  Options.TrapFuncName = CodeGenOpts.TrapFuncName;
  Options.PositionIndependentExecutable = LangOpts.PIELevel != 0;

  TargetMachine *TM = TheTarget->createTargetMachine(Triple, TargetOpts.CPU,
                                                     FeaturesStr, Options,
                                                     RM, CM, OptLevel);

  if (CodeGenOpts.RelaxAll)
    TM->setMCRelaxAll(true);
  if (CodeGenOpts.SaveTempLabels)
    TM->setMCSaveTempLabels(true);
  if (CodeGenOpts.NoDwarf2CFIAsm)
    TM->setMCUseCFI(false);
  if (!CodeGenOpts.NoDwarfDirectoryAsm)
    TM->setMCUseDwarfDirectory(true);
  if (CodeGenOpts.NoExecStack)
    TM->setMCNoExecStack(true);

  // Create the code generator passes.
  PassManager *PM = getCodeGenPasses();

  // Add LibraryInfo.
  TargetLibraryInfo *TLI = new TargetLibraryInfo();
  if (!CodeGenOpts.SimplifyLibCalls)
    TLI->disableAllFunctions();
  PM->add(TLI);

  // Normal mode, emit a .s or .o file by running the code generator. Note,
  // this also adds codegenerator level optimization passes.
  TargetMachine::CodeGenFileType CGFT = TargetMachine::CGFT_AssemblyFile;
  if (Action == Backend_EmitObj)
    CGFT = TargetMachine::CGFT_ObjectFile;
  else if (Action == Backend_EmitMCNull)
    CGFT = TargetMachine::CGFT_Null;
  else
    assert(Action == Backend_EmitAssembly && "Invalid action!");

  // Add ObjC ARC final-cleanup optimizations. This is done as part of the
  // "codegen" passes so that it isn't run multiple times when there is
  // inlining happening.
  if (LangOpts.ObjCAutoRefCount &&
      CodeGenOpts.OptimizationLevel > 0)
    PM->add(createObjCARCContractPass());

  if (TM->addPassesToEmitFile(*PM, OS, CGFT,
                              /*DisableVerify=*/!CodeGenOpts.VerifyModule)) {
    Diags.Report(diag::err_fe_unable_to_interface_with_target);
    return false;
  }

  return true;
}