lib/Driver/Tools.cpp

//===--- Tools.cpp - Tools Implementations ------------------------------*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#include "Tools.h"

#include "clang/Driver/Action.h"
#include "clang/Driver/Arg.h"
#include "clang/Driver/ArgList.h"
#include "clang/Driver/Driver.h" // FIXME: Remove?
#include "clang/Driver/DriverDiagnostic.h" // FIXME: Remove?
#include "clang/Driver/Compilation.h"
#include "clang/Driver/Job.h"
#include "clang/Driver/HostInfo.h"
#include "clang/Driver/Option.h"
#include "clang/Driver/ToolChain.h"
#include "clang/Driver/Util.h"

#include "llvm/ADT/SmallVector.h"
#include "llvm/Support/Format.h"
#include "llvm/Support/raw_ostream.h"

#include "InputInfo.h"
#include "ToolChains.h"

using namespace clang::driver;
using namespace clang::driver::tools;

void Clang::AddPreprocessingOptions(const Driver &D, 
                                    const ArgList &Args,
                                    ArgStringList &CmdArgs,
                                    const InputInfo &Output,
                                    const InputInfoList &Inputs) const {
  // Handle dependency file generation.
  Arg *A;
  if ((A = Args.getLastArg(options::OPT_M)) ||
      (A = Args.getLastArg(options::OPT_MM)) ||
      (A = Args.getLastArg(options::OPT_MD)) ||
      (A = Args.getLastArg(options::OPT_MMD))) {
    // Determine the output location.
    const char *DepFile;
    if (Output.getType() == types::TY_Dependencies) {
      if (Output.isPipe())
        DepFile = "-";
      else
        DepFile = Output.getFilename();
    } else if (Arg *MF = Args.getLastArg(options::OPT_MF)) {
      DepFile = MF->getValue(Args);
    } else if (A->getOption().getId() == options::OPT_M ||
               A->getOption().getId() == options::OPT_MM) {
      DepFile = "-";
    } else {
      DepFile = darwin::CC1::getDependencyFileName(Args, Inputs);
    }
    CmdArgs.push_back("-dependency-file");
    CmdArgs.push_back(DepFile);

    // Add an -MT option if the user didn't specify their own.
    // FIXME: This should use -MQ, when we support it.
    if (!Args.hasArg(options::OPT_MT) && !Args.hasArg(options::OPT_MQ)) {
      const char *DepTarget;

      // If user provided -o, that is the dependency target, except
      // when we are only generating a dependency file.
      Arg *OutputOpt = Args.getLastArg(options::OPT_o);
      if (OutputOpt && Output.getType() != types::TY_Dependencies) {
        DepTarget = OutputOpt->getValue(Args);
      } else {
        // Otherwise derive from the base input.
        //
        // FIXME: This should use the computed output file location.
        llvm::sys::Path P(Inputs[0].getBaseInput());

        P.eraseSuffix();
        P.appendSuffix("o");
        DepTarget = Args.MakeArgString(P.getLast().c_str());
      }

      CmdArgs.push_back("-MT");
      CmdArgs.push_back(DepTarget);
    }

    if (A->getOption().getId() == options::OPT_M ||
        A->getOption().getId() == options::OPT_MD)
      CmdArgs.push_back("-sys-header-deps");
  }

  Args.AddLastArg(CmdArgs, options::OPT_MP);
  Args.AddAllArgs(CmdArgs, options::OPT_MT);

  // FIXME: Use iterator.

  // Add -i* options, and automatically translate to
  // -include-pch/-include-pth for transparent PCH support. It's
  // wonky, but we include looking for .gch so we can support seamless
  // replacement into a build system already set up to be generating
  // .gch files.
  for (ArgList::const_iterator
         it = Args.begin(), ie = Args.end(); it != ie; ++it) {
    const Arg *A = *it;
    if (!A->getOption().matches(options::OPT_clang_i_Group))
      continue;

    if (A->getOption().matches(options::OPT_include)) {
      bool FoundPTH = false;
      bool FoundPCH = false;
      llvm::sys::Path P(A->getValue(Args));
      if (D.CCCUsePCH) {
        P.appendSuffix("pch");
        if (P.exists())
          FoundPCH = true;
        else 
          P.eraseSuffix();
      }

      if (!FoundPCH) {
        P.appendSuffix("pth");
        if (P.exists()) 
          FoundPTH = true;
        else
          P.eraseSuffix();
      } 
      
      if (!FoundPCH && !FoundPTH) {
        P.appendSuffix("gch");
        if (P.exists()) {
          FoundPCH = D.CCCUsePCH;
          FoundPTH = !D.CCCUsePCH;
        }
        else 
          P.eraseSuffix();
      }

      if (FoundPCH || FoundPTH) {
        A->claim();
        if (FoundPCH)
          CmdArgs.push_back("-include-pch");
        else
          CmdArgs.push_back("-include-pth");
        CmdArgs.push_back(Args.MakeArgString(P.c_str()));
        continue;
      }
    }

    // Not translated, render as usual.
    A->claim();
    A->render(Args, CmdArgs);
  }

  Args.AddAllArgs(CmdArgs, options::OPT_D, options::OPT_U);
  Args.AddAllArgs(CmdArgs, options::OPT_I_Group, options::OPT_F);

  // Add -Wp, and -Xassembler if using the preprocessor.

  // FIXME: There is a very unfortunate problem here, some troubled
  // souls abuse -Wp, to pass preprocessor options in gcc syntax. To
  // really support that we would have to parse and then translate
  // those options. :(
  Args.AddAllArgValues(CmdArgs, options::OPT_Wp_COMMA,
                       options::OPT_Xpreprocessor);
}

void Clang::ConstructJob(Compilation &C, const JobAction &JA,
                         Job &Dest,
                         const InputInfo &Output,
                         const InputInfoList &Inputs,
                         const ArgList &Args,
                         const char *LinkingOutput) const {
  const Driver &D = getToolChain().getHost().getDriver();
  ArgStringList CmdArgs;

  assert(Inputs.size() == 1 && "Unable to handle multiple inputs.");

  CmdArgs.push_back("-triple");
  const char *TripleStr =
    Args.MakeArgString(getToolChain().getTripleString().c_str());
  CmdArgs.push_back(TripleStr);

  if (isa<AnalyzeJobAction>(JA)) {
    assert(JA.getType() == types::TY_Plist && "Invalid output type.");
    CmdArgs.push_back("-analyze");
  } else if (isa<PreprocessJobAction>(JA)) {
    if (Output.getType() == types::TY_Dependencies)
      CmdArgs.push_back("-Eonly");
    else
      CmdArgs.push_back("-E");
  } else if (isa<PrecompileJobAction>(JA)) {
    if (D.CCCUsePCH)
      CmdArgs.push_back("-emit-pch");
    else
      CmdArgs.push_back("-emit-pth");
  } else {
    assert(isa<CompileJobAction>(JA) && "Invalid action for clang tool.");

    if (JA.getType() == types::TY_Nothing) {
      CmdArgs.push_back("-fsyntax-only");
    } else if (JA.getType() == types::TY_LLVMAsm) {
      CmdArgs.push_back("-emit-llvm");
    } else if (JA.getType() == types::TY_LLVMBC) {
      CmdArgs.push_back("-emit-llvm-bc");
    } else if (JA.getType() == types::TY_PP_Asm) {
      CmdArgs.push_back("-S");
    }
  }

  // The make clang go fast button.
  CmdArgs.push_back("-disable-free");

  // Set the main file name, so that debug info works even with
  // -save-temps.
  CmdArgs.push_back("-main-file-name");
  CmdArgs.push_back(darwin::CC1::getBaseInputName(Args, Inputs));

  // Some flags which affect the language (via preprocessor
  // defines). See darwin::CC1::AddCPPArgs.
  if (Args.hasArg(options::OPT_static))
    CmdArgs.push_back("-static-define");

  if (isa<AnalyzeJobAction>(JA)) {
    // Add default argument set.
    //
    // FIXME: Move into clang?
    CmdArgs.push_back("-warn-dead-stores");
    CmdArgs.push_back("-checker-cfref");
    CmdArgs.push_back("-analyzer-eagerly-assume");
    CmdArgs.push_back("-warn-objc-methodsigs");
    // Do not enable the missing -dealloc check.
    // '-warn-objc-missing-dealloc',
    CmdArgs.push_back("-warn-objc-unused-ivars");

    CmdArgs.push_back("-analyzer-output=plist");

    // Add -Xanalyzer arguments when running as analyzer.
    Args.AddAllArgValues(CmdArgs, options::OPT_Xanalyzer);
  } else {
    // Perform argument translation for LLVM backend. This
    // takes some care in reconciling with llvm-gcc. The
    // issue is that llvm-gcc translates these options based on
    // the values in cc1, whereas we are processing based on
    // the driver arguments.
    //
    // FIXME: This is currently broken for -f flags when -fno
    // variants are present.

    // This comes from the default translation the driver + cc1
    // would do to enable flag_pic.
    //
    // FIXME: Centralize this code.
    bool PICEnabled = (Args.hasArg(options::OPT_fPIC) ||
                       Args.hasArg(options::OPT_fpic) ||
                       Args.hasArg(options::OPT_fPIE) ||
                       Args.hasArg(options::OPT_fpie));
    bool PICDisabled = (Args.hasArg(options::OPT_mkernel) ||
                        Args.hasArg(options::OPT_static));
    const char *Model = getToolChain().GetForcedPicModel();
    if (!Model) {
      if (Args.hasArg(options::OPT_mdynamic_no_pic))
        Model = "dynamic-no-pic";
      else if (PICDisabled)
        Model = "static";
      else if (PICEnabled)
        Model = "pic";
      else
        Model = getToolChain().GetDefaultRelocationModel();
    }
    CmdArgs.push_back("--relocation-model");
    CmdArgs.push_back(Model);

    // Infer the __PIC__ value.
    //
    // FIXME:  This isn't quite right on Darwin, which always sets
    // __PIC__=2.
    if (strcmp(Model, "pic") == 0 || strcmp(Model, "dynamic-no-pic") == 0) {
      if (Args.hasArg(options::OPT_fPIC))
        CmdArgs.push_back("-pic-level=2");
      else
        CmdArgs.push_back("-pic-level=1");
    }

    if (Args.hasArg(options::OPT_ftime_report))
      CmdArgs.push_back("--time-passes");
    // FIXME: Set --enable-unsafe-fp-math.
    if (!Args.hasArg(options::OPT_fomit_frame_pointer))
      CmdArgs.push_back("--disable-fp-elim");
    if (!Args.hasFlag(options::OPT_fzero_initialized_in_bss,
                      options::OPT_fno_zero_initialized_in_bss,
                      true))
      CmdArgs.push_back("--nozero-initialized-in-bss");
    if (Args.hasArg(options::OPT_dA) || Args.hasArg(options::OPT_fverbose_asm))
      CmdArgs.push_back("--asm-verbose");
    if (Args.hasArg(options::OPT_fdebug_pass_structure))
      CmdArgs.push_back("--debug-pass=Structure");
    if (Args.hasArg(options::OPT_fdebug_pass_arguments))
      CmdArgs.push_back("--debug-pass=Arguments");
    // FIXME: set --inline-threshhold=50 if (optimize_size || optimize
    // < 3)
    if (Args.hasFlag(options::OPT_funwind_tables,
                     options::OPT_fno_unwind_tables,
                     getToolChain().IsUnwindTablesDefault()))
      CmdArgs.push_back("--unwind-tables=1");
    else
      CmdArgs.push_back("--unwind-tables=0");
    if (!Args.hasFlag(options::OPT_mred_zone,
                      options::OPT_mno_red_zone,
                      true))
      CmdArgs.push_back("--disable-red-zone");
    if (Args.hasFlag(options::OPT_msoft_float,
                     options::OPT_mno_soft_float,
                     false))
      CmdArgs.push_back("--soft-float");

    // FIXME: Need target hooks.
    if (memcmp(getToolChain().getPlatform().c_str(), "darwin", 6) == 0) {
      if (getToolChain().getArchName() == "x86_64")
        CmdArgs.push_back("--mcpu=core2");
      else if (getToolChain().getArchName() == "i386")
        CmdArgs.push_back("--mcpu=yonah");
    }

    // FIXME: Ignores ordering. Also, we need to find a realistic
    // solution for this.
    static const struct {
      options::ID Pos, Neg;
      const char *Name;
    } FeatureOptions[] = {
      { options::OPT_mmmx, options::OPT_mno_mmx, "mmx" },
      { options::OPT_msse, options::OPT_mno_sse, "sse" },
      { options::OPT_msse2, options::OPT_mno_sse2, "sse2" },
      { options::OPT_msse3, options::OPT_mno_sse3, "sse3" },
      { options::OPT_mssse3, options::OPT_mno_ssse3, "ssse3" },
      { options::OPT_msse41, options::OPT_mno_sse41, "sse41" },
      { options::OPT_msse42, options::OPT_mno_sse42, "sse42" },
      { options::OPT_msse4a, options::OPT_mno_sse4a, "sse4a" },
      { options::OPT_m3dnow, options::OPT_mno_3dnow, "3dnow" },
      { options::OPT_m3dnowa, options::OPT_mno_3dnowa, "3dnowa" }
    };
    const unsigned NumFeatureOptions =
      sizeof(FeatureOptions)/sizeof(FeatureOptions[0]);

    // FIXME: Avoid std::string
    std::string Attrs;
    for (unsigned i=0; i < NumFeatureOptions; ++i) {
      if (Args.hasArg(FeatureOptions[i].Pos)) {
        if (!Attrs.empty())
          Attrs += ',';
        Attrs += '+';
        Attrs += FeatureOptions[i].Name;
      } else if (Args.hasArg(FeatureOptions[i].Neg)) {
        if (!Attrs.empty())
          Attrs += ',';
        Attrs += '-';
        Attrs += FeatureOptions[i].Name;
      }
    }
    if (!Attrs.empty()) {
      CmdArgs.push_back("--mattr");
      CmdArgs.push_back(Args.MakeArgString(Attrs.c_str()));
    }

    if (Args.hasFlag(options::OPT_fmath_errno,
                     options::OPT_fno_math_errno,
                     getToolChain().IsMathErrnoDefault()))
      CmdArgs.push_back("--fmath-errno=1");
    else
      CmdArgs.push_back("--fmath-errno=0");

    if (Arg *A = Args.getLastArg(options::OPT_flimited_precision_EQ)) {
      CmdArgs.push_back("--limit-float-precision");
      CmdArgs.push_back(A->getValue(Args));
    }

    // FIXME: Add --stack-protector-buffer-size=<xxx> on
    // -fstack-protect.

    Arg *Unsupported;
    if ((Unsupported = Args.getLastArg(options::OPT_MG)) ||
        (Unsupported = Args.getLastArg(options::OPT_MQ)))
      D.Diag(clang::diag::err_drv_unsupported_opt)
        << Unsupported->getOption().getName();
  }

  Args.AddAllArgs(CmdArgs, options::OPT_v);
  Args.AddLastArg(CmdArgs, options::OPT_P);
  Args.AddLastArg(CmdArgs, options::OPT_mmacosx_version_min_EQ);
  Args.AddLastArg(CmdArgs, options::OPT_miphoneos_version_min_EQ);
  Args.AddLastArg(CmdArgs, options::OPT_print_ivar_layout);  

  // Special case debug options to only pass -g to clang. This is
  // wrong.
  if (Args.hasArg(options::OPT_g_Group))
    CmdArgs.push_back("-g");

  Args.AddLastArg(CmdArgs, options::OPT_nostdinc);

  Args.AddLastArg(CmdArgs, options::OPT_isysroot);

  // Add preprocessing options like -I, -D, etc. if we are using the
  // preprocessor.
  //
  // FIXME: Support -fpreprocessed
  types::ID InputType = Inputs[0].getType();
  if (types::getPreprocessedType(InputType) != types::TY_INVALID)
    AddPreprocessingOptions(D, Args, CmdArgs, Output, Inputs);

  // Manually translate -O to -O1 and -O4 to -O3; let clang reject
  // others.
  if (Arg *A = Args.getLastArg(options::OPT_O_Group)) {
    if (A->getOption().getId() == options::OPT_O4)
      CmdArgs.push_back("-O3");
    else if (A->getValue(Args)[0] == '\0')
      CmdArgs.push_back("-O1");
    else
      A->render(Args, CmdArgs);
  }

  Args.AddAllArgs(CmdArgs, options::OPT_W_Group, options::OPT_pedantic_Group);
  Args.AddLastArg(CmdArgs, options::OPT_w);

  // Handle -{std, ansi, trigraphs} -- take the last of -{std, ansi}
  // (-ansi is equivalent to -std=c89).
  //
  // If a std is supplied, only add -trigraphs if it follows the
  // option.
  if (Arg *Std = Args.getLastArg(options::OPT_std_EQ, options::OPT_ansi)) {
    if (Std->getOption().matches(options::OPT_ansi))
      CmdArgs.push_back("-std=c89");
    else
      Std->render(Args, CmdArgs);

    if (Arg *A = Args.getLastArg(options::OPT_trigraphs))
      if (A->getIndex() > Std->getIndex())
        A->render(Args, CmdArgs);
  } else
    Args.AddLastArg(CmdArgs, options::OPT_trigraphs);

  if (Arg *A = Args.getLastArg(options::OPT_ftemplate_depth_)) {
    CmdArgs.push_back("-ftemplate-depth");
    CmdArgs.push_back(A->getValue(Args));
  }

  // Forward -f options which we can pass directly.
  Args.AddLastArg(CmdArgs, options::OPT_femit_all_decls);
  Args.AddLastArg(CmdArgs, options::OPT_fexceptions);
  Args.AddLastArg(CmdArgs, options::OPT_ffreestanding);
  Args.AddLastArg(CmdArgs, options::OPT_fheinous_gnu_extensions);
  Args.AddLastArg(CmdArgs, options::OPT_fgnu_runtime);
  Args.AddLastArg(CmdArgs, options::OPT_flax_vector_conversions);
  Args.AddLastArg(CmdArgs, options::OPT_fms_extensions);
  Args.AddLastArg(CmdArgs, options::OPT_fnext_runtime);
  Args.AddLastArg(CmdArgs, options::OPT_fno_caret_diagnostics);
  Args.AddLastArg(CmdArgs, options::OPT_fno_show_column);
  Args.AddLastArg(CmdArgs, options::OPT_fobjc_gc_only);
  Args.AddLastArg(CmdArgs, options::OPT_fobjc_gc);
  // FIXME: Should we remove this?
  Args.AddLastArg(CmdArgs, options::OPT_fobjc_nonfragile_abi);
  Args.AddLastArg(CmdArgs, options::OPT_fprint_source_range_info);
  Args.AddLastArg(CmdArgs, options::OPT_fdiagnostics_print_source_range_info);
  Args.AddLastArg(CmdArgs, options::OPT_ftime_report);
  Args.AddLastArg(CmdArgs, options::OPT_ftrapv);
  Args.AddLastArg(CmdArgs, options::OPT_fvisibility_EQ);
  Args.AddLastArg(CmdArgs, options::OPT_fwritable_strings);

  // Forward -f options with positive and negative forms; we translate
  // these by hand.

  // -fbuiltin is default, only pass non-default.
  if (!Args.hasFlag(options::OPT_fbuiltin, options::OPT_fno_builtin))
    CmdArgs.push_back("-fbuiltin=0");

  // -fblocks default varies depending on platform and language; only
  // pass if specified.
  if (Arg *A = Args.getLastArg(options::OPT_fblocks, options::OPT_fno_blocks)) {
    if (A->getOption().matches(options::OPT_fblocks))
      CmdArgs.push_back("-fblocks");
    else
      CmdArgs.push_back("-fblocks=0");
  }

  // -fno-pascal-strings is default, only pass non-default. If the
  // -tool chain happened to translate to -mpascal-strings, we want to
  // -back translate here.
  //
  // FIXME: This is gross; that translation should be pulled from the
  // tool chain.
  if (Args.hasFlag(options::OPT_fpascal_strings,
                   options::OPT_fno_pascal_strings,
                   false) ||
      Args.hasFlag(options::OPT_mpascal_strings,
                   options::OPT_mno_pascal_strings,
                   false))
    CmdArgs.push_back("-fpascal-strings");

  // -fcommon is default, only pass non-default.
  if (!Args.hasFlag(options::OPT_fcommon, options::OPT_fno_common))
    CmdArgs.push_back("-fno-common");

  // -fsigned-bitfields is default, and clang doesn't yet support
  // --funsigned-bitfields.
  if (!Args.hasFlag(options::OPT_fsigned_bitfields, 
                    options::OPT_funsigned_bitfields))
    D.Diag(clang::diag::warn_drv_clang_unsupported)
      << Args.getLastArg(options::OPT_funsigned_bitfields)->getAsString(Args);

  // -fdiagnostics-fixit-info is default, only pass non-default.
  if (!Args.hasFlag(options::OPT_fdiagnostics_fixit_info, 
                    options::OPT_fno_diagnostics_fixit_info))
    CmdArgs.push_back("-fno-diagnostics-fixit-info");

  // Enable -fdiagnostics-show-option by default.
  if (Args.hasFlag(options::OPT_fdiagnostics_show_option, 
                   options::OPT_fno_diagnostics_show_option))
    CmdArgs.push_back("-fdiagnostics-show-option");

  // -fdollars-in-identifiers default varies depending on platform and
  // language; only pass if specified.
  if (Arg *A = Args.getLastArg(options::OPT_fdollars_in_identifiers, 
                               options::OPT_fno_dollars_in_identifiers)) {
    if (A->getOption().matches(options::OPT_fdollars_in_identifiers))
      CmdArgs.push_back("-fdollars-in-identifiers=1");
    else
      CmdArgs.push_back("-fdollars-in-identifiers=0");
  }

  Args.AddLastArg(CmdArgs, options::OPT_dM);
  Args.AddLastArg(CmdArgs, options::OPT_dD);

  Args.AddAllArgValues(CmdArgs, options::OPT_Xclang);

  if (Output.getType() == types::TY_Dependencies) {
    // Handled with other dependency code.
  } else if (Output.isPipe()) {
    CmdArgs.push_back("-o");
    CmdArgs.push_back("-");
  } else if (Output.isFilename()) {
    CmdArgs.push_back("-o");
    CmdArgs.push_back(Output.getFilename());
  } else {
    assert(Output.isNothing() && "Invalid output.");
  }

  for (InputInfoList::const_iterator
         it = Inputs.begin(), ie = Inputs.end(); it != ie; ++it) {
    const InputInfo &II = *it;
    CmdArgs.push_back("-x");
    CmdArgs.push_back(types::getTypeName(II.getType()));
    if (II.isPipe())
      CmdArgs.push_back("-");
    else if (II.isFilename())
      CmdArgs.push_back(II.getFilename());
    else
      II.getInputArg().renderAsInput(Args, CmdArgs);
  }

  const char *Exec =
    Args.MakeArgString(getToolChain().GetProgramPath(C, "clang-cc").c_str());
  Dest.addCommand(new Command(Exec, CmdArgs));

  // Explicitly warn that these options are unsupported, even though
  // we are allowing compilation to continue.
  // FIXME: Use iterator.
  for (ArgList::const_iterator
         it = Args.begin(), ie = Args.end(); it != ie; ++it) {
    const Arg *A = *it;
    if (A->getOption().matches(options::OPT_pg)) {
      A->claim();
      D.Diag(clang::diag::warn_drv_clang_unsupported)
        << A->getAsString(Args);
    }
  }

  // Claim some arguments which clang supports automatically.

  // -fpch-preprocess is used with gcc to add a special marker in the
  // -output to include the PCH file. Clang's PTH solution is
  // -completely transparent, so we do not need to deal with it at
  // -all.
  Args.ClaimAllArgs(options::OPT_fpch_preprocess);

  // Claim some arguments which clang doesn't support, but we don't
  // care to warn the user about.

  // FIXME: Use iterator.
  for (ArgList::const_iterator
         it = Args.begin(), ie = Args.end(); it != ie; ++it) {
    const Arg *A = *it;
    if (A->getOption().matches(options::OPT_clang_ignored_f_Group) ||
        A->getOption().matches(options::OPT_clang_ignored_m_Group))
      A->claim();
  }
}

void gcc::Common::ConstructJob(Compilation &C, const JobAction &JA,
                               Job &Dest,
                               const InputInfo &Output,
                               const InputInfoList &Inputs,
                               const ArgList &Args,
                               const char *LinkingOutput) const {
  ArgStringList CmdArgs;

  for (ArgList::const_iterator
         it = Args.begin(), ie = Args.end(); it != ie; ++it) {
    Arg *A = *it;
    if (A->getOption().hasForwardToGCC()) {
      // It is unfortunate that we have to claim here, as this means
      // we will basically never report anything interesting for
      // platforms using a generic gcc.
      A->claim();
      A->render(Args, CmdArgs);
    }
  }

  RenderExtraToolArgs(CmdArgs);

  // If using a driver driver, force the arch.
  if (getToolChain().getHost().useDriverDriver()) {
    CmdArgs.push_back("-arch");

    // FIXME: Remove these special cases.
    const char *Str = getToolChain().getArchName().c_str();
    if (strcmp(Str, "powerpc") == 0)
      Str = "ppc";
    else if (strcmp(Str, "powerpc64") == 0)
      Str = "ppc64";
    CmdArgs.push_back(Str);
  }

  if (Output.isPipe()) {
    CmdArgs.push_back("-o");
    CmdArgs.push_back("-");
  } else if (Output.isFilename()) {
    CmdArgs.push_back("-o");
    CmdArgs.push_back(Output.getFilename());
  } else {
    assert(Output.isNothing() && "Unexpected output");
    CmdArgs.push_back("-fsyntax-only");
  }


  // Only pass -x if gcc will understand it; otherwise hope gcc
  // understands the suffix correctly. The main use case this would go
  // wrong in is for linker inputs if they happened to have an odd
  // suffix; really the only way to get this to happen is a command
  // like '-x foobar a.c' which will treat a.c like a linker input.
  //
  // FIXME: For the linker case specifically, can we safely convert
  // inputs into '-Wl,' options?
  for (InputInfoList::const_iterator
         it = Inputs.begin(), ie = Inputs.end(); it != ie; ++it) {
    const InputInfo &II = *it;
    if (types::canTypeBeUserSpecified(II.getType())) {
      CmdArgs.push_back("-x");
      CmdArgs.push_back(types::getTypeName(II.getType()));
    }

    if (II.isPipe())
      CmdArgs.push_back("-");
    else if (II.isFilename())
      CmdArgs.push_back(II.getFilename());
    else
      // Don't render as input, we need gcc to do the translations.
      II.getInputArg().render(Args, CmdArgs);
  }

  const char *GCCName =
    getToolChain().getHost().getDriver().CCCGenericGCCName.c_str();
  const char *Exec =
    Args.MakeArgString(getToolChain().GetProgramPath(C, GCCName).c_str());
  Dest.addCommand(new Command(Exec, CmdArgs));
}

void gcc::Preprocess::RenderExtraToolArgs(ArgStringList &CmdArgs) const {
  CmdArgs.push_back("-E");
}

void gcc::Precompile::RenderExtraToolArgs(ArgStringList &CmdArgs) const {
  // The type is good enough.
}

void gcc::Compile::RenderExtraToolArgs(ArgStringList &CmdArgs) const {
  CmdArgs.push_back("-S");
}

void gcc::Assemble::RenderExtraToolArgs(ArgStringList &CmdArgs) const {
  CmdArgs.push_back("-c");
}

void gcc::Link::RenderExtraToolArgs(ArgStringList &CmdArgs) const {
  // The types are (hopefully) good enough.
}

const char *darwin::CC1::getCC1Name(types::ID Type) const {
  switch (Type) {
  default:
    assert(0 && "Unexpected type for Darwin CC1 tool.");
  case types::TY_Asm:
  case types::TY_C: case types::TY_CHeader:
  case types::TY_PP_C: case types::TY_PP_CHeader:
    return "cc1";
  case types::TY_ObjC: case types::TY_ObjCHeader:
  case types::TY_PP_ObjC: case types::TY_PP_ObjCHeader:
    return "cc1obj";
  case types::TY_CXX: case types::TY_CXXHeader:
  case types::TY_PP_CXX: case types::TY_PP_CXXHeader:
    return "cc1plus";
  case types::TY_ObjCXX: case types::TY_ObjCXXHeader:
  case types::TY_PP_ObjCXX: case types::TY_PP_ObjCXXHeader:
    return "cc1objplus";
  }
}

const char *darwin::CC1::getBaseInputName(const ArgList &Args,
                                          const InputInfoList &Inputs) {
  llvm::sys::Path P(Inputs[0].getBaseInput());
  return Args.MakeArgString(P.getLast().c_str());
}

const char *darwin::CC1::getBaseInputStem(const ArgList &Args,
                                          const InputInfoList &Inputs) {
  const char *Str = getBaseInputName(Args, Inputs);

  if (const char *End = strchr(Str, '.'))
    return Args.MakeArgString(std::string(Str, End).c_str());

  return Str;
}

const char *
darwin::CC1::getDependencyFileName(const ArgList &Args,
                                   const InputInfoList &Inputs) {
  // FIXME: Think about this more.
  std::string Res;

  if (Arg *OutputOpt = Args.getLastArg(options::OPT_o)) {
    std::string Str(OutputOpt->getValue(Args));

    Res = Str.substr(0, Str.rfind('.'));
  } else
    Res = darwin::CC1::getBaseInputStem(Args, Inputs);

  return Args.MakeArgString((Res + ".d").c_str());
}

void darwin::CC1::AddCC1Args(const ArgList &Args,
                             ArgStringList &CmdArgs) const {
  // Derived from cc1 spec.

  // FIXME: -fapple-kext seems to disable this too. Investigate.
  if (!Args.hasArg(options::OPT_mkernel) && !Args.hasArg(options::OPT_static) &&
      !Args.hasArg(options::OPT_mdynamic_no_pic))
    CmdArgs.push_back("-fPIC");

  // gcc has some code here to deal with when no -mmacosx-version-min
  // and no -miphoneos-version-min is present, but this never happens
  // due to tool chain specific argument translation.

  // FIXME: Remove mthumb
  // FIXME: Remove mno-thumb
  // FIXME: Remove faltivec
  // FIXME: Remove mno-fused-madd
  // FIXME: Remove mlong-branch
  // FIXME: Remove mlongcall
  // FIXME: Remove mcpu=G4
  // FIXME: Remove mcpu=G5

  if (Args.hasArg(options::OPT_g_Flag) &&
      !Args.hasArg(options::OPT_fno_eliminate_unused_debug_symbols))
    CmdArgs.push_back("-feliminate-unused-debug-symbols");
}

void darwin::CC1::AddCC1OptionsArgs(const ArgList &Args, ArgStringList &CmdArgs,
                                    const InputInfoList &Inputs,
                                    const ArgStringList &OutputArgs) const {
  const Driver &D = getToolChain().getHost().getDriver();

  // Derived from cc1_options spec.
  if (Args.hasArg(options::OPT_fast) ||
      Args.hasArg(options::OPT_fastf) ||
      Args.hasArg(options::OPT_fastcp))
    CmdArgs.push_back("-O3");

  if (Arg *A = Args.getLastArg(options::OPT_pg))
    if (Args.hasArg(options::OPT_fomit_frame_pointer))
      D.Diag(clang::diag::err_drv_argument_not_allowed_with)
        << A->getAsString(Args) << "-fomit-frame-pointer";

  AddCC1Args(Args, CmdArgs);

  if (!Args.hasArg(options::OPT_Q))
    CmdArgs.push_back("-quiet");

  CmdArgs.push_back("-dumpbase");
  CmdArgs.push_back(darwin::CC1::getBaseInputName(Args, Inputs));

  Args.AddAllArgs(CmdArgs, options::OPT_d_Group);

  Args.AddAllArgs(CmdArgs, options::OPT_m_Group);
  Args.AddAllArgs(CmdArgs, options::OPT_a_Group);

  // FIXME: The goal is to use the user provided -o if that is our
  // final output, otherwise to drive from the original input
  // name. Find a clean way to go about this.
  if ((Args.hasArg(options::OPT_c) || Args.hasArg(options::OPT_S)) &&
      Args.hasArg(options::OPT_o)) {
    Arg *OutputOpt = Args.getLastArg(options::OPT_o);
    CmdArgs.push_back("-auxbase-strip");
    CmdArgs.push_back(OutputOpt->getValue(Args));
  } else {
    CmdArgs.push_back("-auxbase");
    CmdArgs.push_back(darwin::CC1::getBaseInputStem(Args, Inputs));
  }

  Args.AddAllArgs(CmdArgs, options::OPT_g_Group);

  Args.AddAllArgs(CmdArgs, options::OPT_O);
  // FIXME: -Wall is getting some special treatment. Investigate.
  Args.AddAllArgs(CmdArgs, options::OPT_W_Group, options::OPT_pedantic_Group);
  Args.AddLastArg(CmdArgs, options::OPT_w);
  Args.AddAllArgs(CmdArgs, options::OPT_std_EQ, options::OPT_ansi,
                  options::OPT_trigraphs);
  if (Args.hasArg(options::OPT_v))
    CmdArgs.push_back("-version");
  if (Args.hasArg(options::OPT_pg))
    CmdArgs.push_back("-p");
  Args.AddLastArg(CmdArgs, options::OPT_p);

  // The driver treats -fsyntax-only specially.
  Args.AddAllArgs(CmdArgs, options::OPT_f_Group, options::OPT_fsyntax_only);

  Args.AddAllArgs(CmdArgs, options::OPT_undef);
  if (Args.hasArg(options::OPT_Qn))
    CmdArgs.push_back("-fno-ident");

  // FIXME: This isn't correct.
  //Args.AddLastArg(CmdArgs, options::OPT__help)
  //Args.AddLastArg(CmdArgs, options::OPT__targetHelp)

  CmdArgs.append(OutputArgs.begin(), OutputArgs.end());

  // FIXME: Still don't get what is happening here. Investigate.
  Args.AddAllArgs(CmdArgs, options::OPT__param);

  if (Args.hasArg(options::OPT_fmudflap) ||
      Args.hasArg(options::OPT_fmudflapth)) {
    CmdArgs.push_back("-fno-builtin");
    CmdArgs.push_back("-fno-merge-constants");
  }

  if (Args.hasArg(options::OPT_coverage)) {
    CmdArgs.push_back("-fprofile-arcs");
    CmdArgs.push_back("-ftest-coverage");
  }

  if (types::isCXX(Inputs[0].getType()))
    CmdArgs.push_back("-D__private_extern__=extern");
}

void darwin::CC1::AddCPPOptionsArgs(const ArgList &Args, ArgStringList &CmdArgs,
                                    const InputInfoList &Inputs,
                                    const ArgStringList &OutputArgs) const {
  // Derived from cpp_options
  AddCPPUniqueOptionsArgs(Args, CmdArgs, Inputs);

  CmdArgs.append(OutputArgs.begin(), OutputArgs.end());

  AddCC1Args(Args, CmdArgs);

  // NOTE: The code below has some commonality with cpp_options, but
  // in classic gcc style ends up sending things in different
  // orders. This may be a good merge candidate once we drop pedantic
  // compatibility.

  Args.AddAllArgs(CmdArgs, options::OPT_m_Group);
  Args.AddAllArgs(CmdArgs, options::OPT_std_EQ, options::OPT_ansi,
                  options::OPT_trigraphs);
  Args.AddAllArgs(CmdArgs, options::OPT_W_Group, options::OPT_pedantic_Group);
  Args.AddLastArg(CmdArgs, options::OPT_w);

  // The driver treats -fsyntax-only specially.
  Args.AddAllArgs(CmdArgs, options::OPT_f_Group, options::OPT_fsyntax_only);

  if (Args.hasArg(options::OPT_g_Group) && !Args.hasArg(options::OPT_g0) &&
      !Args.hasArg(options::OPT_fno_working_directory))
    CmdArgs.push_back("-fworking-directory");

  Args.AddAllArgs(CmdArgs, options::OPT_O);
  Args.AddAllArgs(CmdArgs, options::OPT_undef);
  if (Args.hasArg(options::OPT_save_temps))
    CmdArgs.push_back("-fpch-preprocess");
}

void darwin::CC1::AddCPPUniqueOptionsArgs(const ArgList &Args,
                                          ArgStringList &CmdArgs,
                                          const InputInfoList &Inputs) const
{
  const Driver &D = getToolChain().getHost().getDriver();

  // Derived from cpp_unique_options.
  Arg *A;
  if ((A = Args.getLastArg(options::OPT_C)) ||
      (A = Args.getLastArg(options::OPT_CC))) {
    if (!Args.hasArg(options::OPT_E))
      D.Diag(clang::diag::err_drv_argument_only_allowed_with)
        << A->getAsString(Args) << "-E";
  }
  if (!Args.hasArg(options::OPT_Q))
    CmdArgs.push_back("-quiet");
  Args.AddAllArgs(CmdArgs, options::OPT_nostdinc);
  Args.AddLastArg(CmdArgs, options::OPT_v);
  Args.AddAllArgs(CmdArgs, options::OPT_I_Group, options::OPT_F);
  Args.AddLastArg(CmdArgs, options::OPT_P);

  // FIXME: Handle %I properly.
  if (getToolChain().getArchName() == "x86_64") {
    CmdArgs.push_back("-imultilib");
    CmdArgs.push_back("x86_64");
  }

  if (Args.hasArg(options::OPT_MD)) {
    CmdArgs.push_back("-MD");
    CmdArgs.push_back(darwin::CC1::getDependencyFileName(Args, Inputs));
  }

  if (Args.hasArg(options::OPT_MMD)) {
    CmdArgs.push_back("-MMD");
    CmdArgs.push_back(darwin::CC1::getDependencyFileName(Args, Inputs));
  }

  Args.AddLastArg(CmdArgs, options::OPT_M);
  Args.AddLastArg(CmdArgs, options::OPT_MM);
  Args.AddAllArgs(CmdArgs, options::OPT_MF);
  Args.AddLastArg(CmdArgs, options::OPT_MG);
  Args.AddLastArg(CmdArgs, options::OPT_MP);
  Args.AddAllArgs(CmdArgs, options::OPT_MQ);
  Args.AddAllArgs(CmdArgs, options::OPT_MT);
  if (!Args.hasArg(options::OPT_M) && !Args.hasArg(options::OPT_MM) &&
      (Args.hasArg(options::OPT_MD) || Args.hasArg(options::OPT_MMD))) {
    if (Arg *OutputOpt = Args.getLastArg(options::OPT_o)) {
      CmdArgs.push_back("-MQ");
      CmdArgs.push_back(OutputOpt->getValue(Args));
    }
  }

  Args.AddLastArg(CmdArgs, options::OPT_remap);
  if (Args.hasArg(options::OPT_g3))
    CmdArgs.push_back("-dD");
  Args.AddLastArg(CmdArgs, options::OPT_H);

  AddCPPArgs(Args, CmdArgs);

  Args.AddAllArgs(CmdArgs, options::OPT_D, options::OPT_U, options::OPT_A);
  Args.AddAllArgs(CmdArgs, options::OPT_i_Group);

  for (InputInfoList::const_iterator
         it = Inputs.begin(), ie = Inputs.end(); it != ie; ++it) {
    const InputInfo &II = *it;

    if (II.isPipe())
      CmdArgs.push_back("-");
    else
      CmdArgs.push_back(II.getFilename());
  }

  Args.AddAllArgValues(CmdArgs, options::OPT_Wp_COMMA,
                       options::OPT_Xpreprocessor);

  if (Args.hasArg(options::OPT_fmudflap)) {
    CmdArgs.push_back("-D_MUDFLAP");
    CmdArgs.push_back("-include");
    CmdArgs.push_back("mf-runtime.h");
  }

  if (Args.hasArg(options::OPT_fmudflapth)) {
    CmdArgs.push_back("-D_MUDFLAP");
    CmdArgs.push_back("-D_MUDFLAPTH");
    CmdArgs.push_back("-include");
    CmdArgs.push_back("mf-runtime.h");
  }
}

void darwin::CC1::AddCPPArgs(const ArgList &Args,
                             ArgStringList &CmdArgs) const {
  // Derived from cpp spec.

  if (Args.hasArg(options::OPT_static)) {
    // The gcc spec is broken here, it refers to dynamic but
    // that has been translated. Start by being bug compatible.

    // if (!Args.hasArg(arglist.parser.dynamicOption))
    CmdArgs.push_back("-D__STATIC__");
  } else
    CmdArgs.push_back("-D__DYNAMIC__");

  if (Args.hasArg(options::OPT_pthread))
    CmdArgs.push_back("-D_REENTRANT");
}

void darwin::Preprocess::ConstructJob(Compilation &C, const JobAction &JA,
                                      Job &Dest, const InputInfo &Output,
                                      const InputInfoList &Inputs,
                                      const ArgList &Args,
                                      const char *LinkingOutput) const {
  ArgStringList CmdArgs;

  assert(Inputs.size() == 1 && "Unexpected number of inputs!");

  CmdArgs.push_back("-E");

  if (Args.hasArg(options::OPT_traditional) ||
      Args.hasArg(options::OPT_ftraditional) ||
      Args.hasArg(options::OPT_traditional_cpp))
    CmdArgs.push_back("-traditional-cpp");

  ArgStringList OutputArgs;
  if (Output.isFilename()) {
    OutputArgs.push_back("-o");
    OutputArgs.push_back(Output.getFilename());
  } else {
    assert(Output.isPipe() && "Unexpected CC1 output.");
  }

  if (Args.hasArg(options::OPT_E)) {
    AddCPPOptionsArgs(Args, CmdArgs, Inputs, OutputArgs);
  } else {
    AddCPPOptionsArgs(Args, CmdArgs, Inputs, ArgStringList());
    CmdArgs.append(OutputArgs.begin(), OutputArgs.end());
  }

  Args.AddAllArgs(CmdArgs, options::OPT_d_Group);

  const char *CC1Name = getCC1Name(Inputs[0].getType());
  const char *Exec =
    Args.MakeArgString(getToolChain().GetProgramPath(C, CC1Name).c_str());
  Dest.addCommand(new Command(Exec, CmdArgs));
}

void darwin::Compile::ConstructJob(Compilation &C, const JobAction &JA,
                                   Job &Dest, const InputInfo &Output,
                                   const InputInfoList &Inputs,
                                   const ArgList &Args,
                                   const char *LinkingOutput) const {
  const Driver &D = getToolChain().getHost().getDriver();
  ArgStringList CmdArgs;

  assert(Inputs.size() == 1 && "Unexpected number of inputs!");

  types::ID InputType = Inputs[0].getType();
  const Arg *A;
  if ((A = Args.getLastArg(options::OPT_traditional)) ||
      (A = Args.getLastArg(options::OPT_ftraditional)))
    D.Diag(clang::diag::err_drv_argument_only_allowed_with)
      << A->getAsString(Args) << "-E";

  if (Output.getType() == types::TY_LLVMAsm)
    CmdArgs.push_back("-emit-llvm");
  else if (Output.getType() == types::TY_LLVMBC)
    CmdArgs.push_back("-emit-llvm-bc");

  ArgStringList OutputArgs;
  if (Output.getType() != types::TY_PCH) {
    OutputArgs.push_back("-o");
    if (Output.isPipe())
      OutputArgs.push_back("-");
    else if (Output.isNothing())
      OutputArgs.push_back("/dev/null");
    else
      OutputArgs.push_back(Output.getFilename());
  }

  // There is no need for this level of compatibility, but it makes
  // diffing easier.
  bool OutputArgsEarly = (Args.hasArg(options::OPT_fsyntax_only) ||
                          Args.hasArg(options::OPT_S));

  if (types::getPreprocessedType(InputType) != types::TY_INVALID) {
    AddCPPUniqueOptionsArgs(Args, CmdArgs, Inputs);
    if (OutputArgsEarly) {
      AddCC1OptionsArgs(Args, CmdArgs, Inputs, OutputArgs);
    } else {
      AddCC1OptionsArgs(Args, CmdArgs, Inputs, ArgStringList());
      CmdArgs.append(OutputArgs.begin(), OutputArgs.end());
    }
  } else {
    CmdArgs.push_back("-fpreprocessed");

    // FIXME: There is a spec command to remove
    // -fpredictive-compilation args here. Investigate.

    for (InputInfoList::const_iterator
           it = Inputs.begin(), ie = Inputs.end(); it != ie; ++it) {
      const InputInfo &II = *it;

      if (II.isPipe())
        CmdArgs.push_back("-");
      else
        CmdArgs.push_back(II.getFilename());
    }

    if (OutputArgsEarly) {
      AddCC1OptionsArgs(Args, CmdArgs, Inputs, OutputArgs);
    } else {
      AddCC1OptionsArgs(Args, CmdArgs, Inputs, ArgStringList());
      CmdArgs.append(OutputArgs.begin(), OutputArgs.end());
    }
  }

  if (Output.getType() == types::TY_PCH) {
    assert(Output.isFilename() && "Invalid PCH output.");

    CmdArgs.push_back("-o");
    // NOTE: gcc uses a temp .s file for this, but there doesn't seem
    // to be a good reason.
    CmdArgs.push_back("/dev/null");

    CmdArgs.push_back("--output-pch=");
    CmdArgs.push_back(Output.getFilename());
  }

  const char *CC1Name = getCC1Name(Inputs[0].getType());
  const char *Exec =
    Args.MakeArgString(getToolChain().GetProgramPath(C, CC1Name).c_str());
  Dest.addCommand(new Command(Exec, CmdArgs));
}

void darwin::Assemble::ConstructJob(Compilation &C, const JobAction &JA,
                                    Job &Dest, const InputInfo &Output,
                                    const InputInfoList &Inputs,
                                    const ArgList &Args,
                                    const char *LinkingOutput) const {
  ArgStringList CmdArgs;

  assert(Inputs.size() == 1 && "Unexpected number of inputs.");
  const InputInfo &Input = Inputs[0];

  // Bit of a hack, this is only used for original inputs.
  //
  // FIXME: This is broken for preprocessed .s inputs.
  if (Input.isFilename() &&
      strcmp(Input.getFilename(), Input.getBaseInput()) == 0) {
    if (Args.hasArg(options::OPT_gstabs))
      CmdArgs.push_back("--gstabs");
    else if (Args.hasArg(options::OPT_g_Group))
      CmdArgs.push_back("--gdwarf2");
  }

  // Derived from asm spec.
  CmdArgs.push_back("-arch");
  CmdArgs.push_back(getToolChain().getArchName().c_str());

  CmdArgs.push_back("-force_cpusubtype_ALL");
  if ((Args.hasArg(options::OPT_mkernel) ||
       Args.hasArg(options::OPT_static) ||
       Args.hasArg(options::OPT_fapple_kext)) &&
      !Args.hasArg(options::OPT_dynamic))
    CmdArgs.push_back("-static");

  Args.AddAllArgValues(CmdArgs, options::OPT_Wa_COMMA,
                       options::OPT_Xassembler);

  assert(Output.isFilename() && "Unexpected lipo output.");
  CmdArgs.push_back("-o");
  CmdArgs.push_back(Output.getFilename());

  if (Input.isPipe()) {
    CmdArgs.push_back("-");
  } else {
    assert(Input.isFilename() && "Invalid input.");
    CmdArgs.push_back(Input.getFilename());
  }

  // asm_final spec is empty.

  const char *Exec =
    Args.MakeArgString(getToolChain().GetProgramPath(C, "as").c_str());
  Dest.addCommand(new Command(Exec, CmdArgs));
}

static const char *MakeFormattedString(const ArgList &Args,
                                       const llvm::format_object_base &Fmt) {
  std::string Str;
  llvm::raw_string_ostream(Str) << Fmt;
  return Args.MakeArgString(Str.c_str());
}

/// Helper routine for seeing if we should use dsymutil; this is a
/// gcc compatible hack, we should remove it and use the input
/// type information.
static bool isSourceSuffix(const char *Str) {
  // match: 'C', 'CPP', 'c', 'cc', 'cp', 'c++', 'cpp', 'cxx', 'm',
  // 'mm'.
  switch (strlen(Str)) {
  default:
    return false;
  case 1:
    return (memcmp(Str, "C", 1) == 0 ||
            memcmp(Str, "c", 1) == 0 ||
            memcmp(Str, "m", 1) == 0);
  case 2:
    return (memcmp(Str, "cc", 2) == 0 ||
            memcmp(Str, "cp", 2) == 0 ||
            memcmp(Str, "mm", 2) == 0);
  case 3:
    return (memcmp(Str, "CPP", 3) == 0 ||
            memcmp(Str, "c++", 3) == 0 ||
            memcmp(Str, "cpp", 3) == 0 ||
            memcmp(Str, "cxx", 3) == 0);
  }
}

static bool isMacosxVersionLT(unsigned (&A)[3], unsigned (&B)[3]) {
  for (unsigned i=0; i < 3; ++i) {
    if (A[i] > B[i]) return false;
    if (A[i] < B[i]) return true;
  }
  return false;
}

static bool isMacosxVersionLT(unsigned (&A)[3],
                              unsigned V0, unsigned V1=0, unsigned V2=0) {
  unsigned B[3] = { V0, V1, V2 };
  return isMacosxVersionLT(A, B);
}

const toolchains::Darwin_X86 &darwin::Link::getDarwinToolChain() const {
  return reinterpret_cast<const toolchains::Darwin_X86&>(getToolChain());
}

void darwin::Link::AddDarwinArch(const ArgList &Args,
                                 ArgStringList &CmdArgs) const {
  // Derived from darwin_arch spec.
  CmdArgs.push_back("-arch");
  CmdArgs.push_back(getToolChain().getArchName().c_str());
}

void darwin::Link::AddDarwinSubArch(const ArgList &Args,
                                    ArgStringList &CmdArgs) const {
  // Derived from darwin_subarch spec, not sure what the distinction
  // exists for but at least for this chain it is the same.
  AddDarwinArch(Args, CmdArgs);
}

void darwin::Link::AddLinkArgs(const ArgList &Args,
                               ArgStringList &CmdArgs) const {
  const Driver &D = getToolChain().getHost().getDriver();

  // Derived from the "link" spec.
  Args.AddAllArgs(CmdArgs, options::OPT_static);
  if (!Args.hasArg(options::OPT_static))
    CmdArgs.push_back("-dynamic");
  if (Args.hasArg(options::OPT_fgnu_runtime)) {
    // FIXME: gcc replaces -lobjc in forward args with -lobjc-gnu
    // here. How do we wish to handle such things?
  }

  if (!Args.hasArg(options::OPT_dynamiclib)) {
    if (Args.hasArg(options::OPT_force__cpusubtype__ALL)) {
      AddDarwinArch(Args, CmdArgs);
      CmdArgs.push_back("-force_cpusubtype_ALL");
    } else
      AddDarwinSubArch(Args, CmdArgs);

    Args.AddLastArg(CmdArgs, options::OPT_bundle);
    Args.AddAllArgs(CmdArgs, options::OPT_bundle__loader);
    Args.AddAllArgs(CmdArgs, options::OPT_client__name);

    Arg *A;
    if ((A = Args.getLastArg(options::OPT_compatibility__version)) ||
        (A = Args.getLastArg(options::OPT_current__version)) ||
        (A = Args.getLastArg(options::OPT_install__name)))
      D.Diag(clang::diag::err_drv_argument_only_allowed_with)
        << A->getAsString(Args) << "-dynamiclib";

    Args.AddLastArg(CmdArgs, options::OPT_force__flat__namespace);
    Args.AddLastArg(CmdArgs, options::OPT_keep__private__externs);
    Args.AddLastArg(CmdArgs, options::OPT_private__bundle);
  } else {
    CmdArgs.push_back("-dylib");

    Arg *A;
    if ((A = Args.getLastArg(options::OPT_bundle)) ||
        (A = Args.getLastArg(options::OPT_bundle__loader)) ||
        (A = Args.getLastArg(options::OPT_client__name)) ||
        (A = Args.getLastArg(options::OPT_force__flat__namespace)) ||
        (A = Args.getLastArg(options::OPT_keep__private__externs)) ||
        (A = Args.getLastArg(options::OPT_private__bundle)))
      D.Diag(clang::diag::err_drv_argument_not_allowed_with)
        << A->getAsString(Args) << "-dynamiclib";

    Args.AddAllArgsTranslated(CmdArgs, options::OPT_compatibility__version,
                              "-dylib_compatibility_version");
    Args.AddAllArgsTranslated(CmdArgs, options::OPT_current__version,
                              "-dylib_current_version");

    if (Args.hasArg(options::OPT_force__cpusubtype__ALL)) {
      AddDarwinArch(Args, CmdArgs);
      // NOTE: We don't add -force_cpusubtype_ALL on this path. Ok.
    } else
      AddDarwinSubArch(Args, CmdArgs);

    Args.AddAllArgsTranslated(CmdArgs, options::OPT_install__name,
                              "-dylib_install_name");
  }

  Args.AddLastArg(CmdArgs, options::OPT_all__load);
  Args.AddAllArgs(CmdArgs, options::OPT_allowable__client);
  Args.AddLastArg(CmdArgs, options::OPT_bind__at__load);
  Args.AddLastArg(CmdArgs, options::OPT_dead__strip);
  Args.AddLastArg(CmdArgs, options::OPT_no__dead__strip__inits__and__terms);
  Args.AddAllArgs(CmdArgs, options::OPT_dylib__file);
  Args.AddLastArg(CmdArgs, options::OPT_dynamic);
  Args.AddAllArgs(CmdArgs, options::OPT_exported__symbols__list);
  Args.AddLastArg(CmdArgs, options::OPT_flat__namespace);
  Args.AddAllArgs(CmdArgs, options::OPT_headerpad__max__install__names);
  Args.AddAllArgs(CmdArgs, options::OPT_image__base);
  Args.AddAllArgs(CmdArgs, options::OPT_init);

  if (!Args.hasArg(options::OPT_mmacosx_version_min_EQ)) {
    if (!Args.hasArg(options::OPT_miphoneos_version_min_EQ)) {
      // FIXME: I don't understand what is going on here. This is
      // supposed to come from darwin_ld_minversion, but gcc doesn't
      // seem to be following that; it must be getting overridden
      // somewhere.
      CmdArgs.push_back("-macosx_version_min");
      CmdArgs.push_back(getDarwinToolChain().getMacosxVersionStr());
    }
  } else {
    // Adding all arguments doesn't make sense here but this is what
    // gcc does.
    Args.AddAllArgsTranslated(CmdArgs, options::OPT_mmacosx_version_min_EQ,
                              "-macosx_version_min");
  }

  Args.AddAllArgsTranslated(CmdArgs, options::OPT_miphoneos_version_min_EQ,
                            "-iphoneos_version_min");
  Args.AddLastArg(CmdArgs, options::OPT_nomultidefs);
  Args.AddLastArg(CmdArgs, options::OPT_multi__module);
  Args.AddLastArg(CmdArgs, options::OPT_single__module);
  Args.AddAllArgs(CmdArgs, options::OPT_multiply__defined);
  Args.AddAllArgs(CmdArgs, options::OPT_multiply__defined__unused);

  if (Args.hasArg(options::OPT_fpie))
    CmdArgs.push_back("-pie");

  Args.AddLastArg(CmdArgs, options::OPT_prebind);
  Args.AddLastArg(CmdArgs, options::OPT_noprebind);
  Args.AddLastArg(CmdArgs, options::OPT_nofixprebinding);
  Args.AddLastArg(CmdArgs, options::OPT_prebind__all__twolevel__modules);
  Args.AddLastArg(CmdArgs, options::OPT_read__only__relocs);
  Args.AddAllArgs(CmdArgs, options::OPT_sectcreate);
  Args.AddAllArgs(CmdArgs, options::OPT_sectorder);
  Args.AddAllArgs(CmdArgs, options::OPT_seg1addr);
  Args.AddAllArgs(CmdArgs, options::OPT_segprot);
  Args.AddAllArgs(CmdArgs, options::OPT_segaddr);
  Args.AddAllArgs(CmdArgs, options::OPT_segs__read__only__addr);
  Args.AddAllArgs(CmdArgs, options::OPT_segs__read__write__addr);
  Args.AddAllArgs(CmdArgs, options::OPT_seg__addr__table);
  Args.AddAllArgs(CmdArgs, options::OPT_seg__addr__table__filename);
  Args.AddAllArgs(CmdArgs, options::OPT_sub__library);
  Args.AddAllArgs(CmdArgs, options::OPT_sub__umbrella);
  Args.AddAllArgsTranslated(CmdArgs, options::OPT_isysroot, "-syslibroot");
  Args.AddLastArg(CmdArgs, options::OPT_twolevel__namespace);
  Args.AddLastArg(CmdArgs, options::OPT_twolevel__namespace__hints);
  Args.AddAllArgs(CmdArgs, options::OPT_umbrella);
  Args.AddAllArgs(CmdArgs, options::OPT_undefined);
  Args.AddAllArgs(CmdArgs, options::OPT_unexported__symbols__list);
  Args.AddAllArgs(CmdArgs, options::OPT_weak__reference__mismatches);

  if (!Args.hasArg(options::OPT_weak__reference__mismatches)) {
    CmdArgs.push_back("-weak_reference_mismatches");
    CmdArgs.push_back("non-weak");
  }

  Args.AddLastArg(CmdArgs, options::OPT_X_Flag);
  Args.AddAllArgs(CmdArgs, options::OPT_y);
  Args.AddLastArg(CmdArgs, options::OPT_w);
  Args.AddAllArgs(CmdArgs, options::OPT_pagezero__size);
  Args.AddAllArgs(CmdArgs, options::OPT_segs__read__);
  Args.AddLastArg(CmdArgs, options::OPT_seglinkedit);
  Args.AddLastArg(CmdArgs, options::OPT_noseglinkedit);
  Args.AddAllArgs(CmdArgs, options::OPT_sectalign);
  Args.AddAllArgs(CmdArgs, options::OPT_sectobjectsymbols);
  Args.AddAllArgs(CmdArgs, options::OPT_segcreate);
  Args.AddLastArg(CmdArgs, options::OPT_whyload);
  Args.AddLastArg(CmdArgs, options::OPT_whatsloaded);
  Args.AddAllArgs(CmdArgs, options::OPT_dylinker__install__name);
  Args.AddLastArg(CmdArgs, options::OPT_dylinker);
  Args.AddLastArg(CmdArgs, options::OPT_Mach);
}

void darwin::Link::ConstructJob(Compilation &C, const JobAction &JA,
                                Job &Dest, const InputInfo &Output,
                                const InputInfoList &Inputs,
                                const ArgList &Args,
                                const char *LinkingOutput) const {
  assert(Output.getType() == types::TY_Image && "Invalid linker output type.");
  // The logic here is derived from gcc's behavior; most of which
  // comes from specs (starting with link_command). Consult gcc for
  // more information.

  // FIXME: The spec references -fdump= which seems to have
  // disappeared?

  ArgStringList CmdArgs;

  // I'm not sure why this particular decomposition exists in gcc, but
  // we follow suite for ease of comparison.
  AddLinkArgs(Args, CmdArgs);

  // FIXME: gcc has %{x} in here. How could this ever happen?  Cruft?
  Args.AddAllArgs(CmdArgs, options::OPT_d_Flag);
  Args.AddAllArgs(CmdArgs, options::OPT_s);
  Args.AddAllArgs(CmdArgs, options::OPT_t);
  Args.AddAllArgs(CmdArgs, options::OPT_Z_Flag);
  Args.AddAllArgs(CmdArgs, options::OPT_u_Group);
  Args.AddAllArgs(CmdArgs, options::OPT_A);
  Args.AddLastArg(CmdArgs, options::OPT_e);
  Args.AddAllArgs(CmdArgs, options::OPT_m_Separate);
  Args.AddAllArgs(CmdArgs, options::OPT_r);

  // FIXME: This is just being pedantically bug compatible, gcc
  // doesn't *mean* to forward this, it just does (yay for pattern
  // matching). It doesn't work, of course.
  Args.AddAllArgs(CmdArgs, options::OPT_object);

  CmdArgs.push_back("-o");
  CmdArgs.push_back(Output.getFilename());

  unsigned MacosxVersion[3];
  if (Arg *A = Args.getLastArg(options::OPT_mmacosx_version_min_EQ)) {
    bool HadExtra;
    if (!Driver::GetReleaseVersion(A->getValue(Args), MacosxVersion[0],
                                   MacosxVersion[1], MacosxVersion[2],
                                   HadExtra) ||
        HadExtra) {
      const Driver &D = getToolChain().getHost().getDriver();
      D.Diag(clang::diag::err_drv_invalid_version_number)
        << A->getAsString(Args);
    }
  } else {
    getDarwinToolChain().getMacosxVersion(MacosxVersion);
  }

  if (!Args.hasArg(options::OPT_A) &&
      !Args.hasArg(options::OPT_nostdlib) &&
      !Args.hasArg(options::OPT_nostartfiles)) {
    // Derived from startfile spec.
    if (Args.hasArg(options::OPT_dynamiclib)) {
      // Derived from darwin_dylib1 spec.
      if (isMacosxVersionLT(MacosxVersion, 10, 5))
        CmdArgs.push_back("-ldylib1.o");
      else if (isMacosxVersionLT(MacosxVersion, 10, 6))
        CmdArgs.push_back("-ldylib1.10.5.o");
    } else {
      if (Args.hasArg(options::OPT_bundle)) {
        if (!Args.hasArg(options::OPT_static)) {
          // Derived from darwin_bundle1 spec.
          if (isMacosxVersionLT(MacosxVersion, 10, 6))
            CmdArgs.push_back("-lbundle1.o");
        }
      } else {
        if (Args.hasArg(options::OPT_pg)) {
          if (Args.hasArg(options::OPT_static) ||
              Args.hasArg(options::OPT_object) ||
              Args.hasArg(options::OPT_preload)) {
            CmdArgs.push_back("-lgcrt0.o");
          } else {
            CmdArgs.push_back("-lgcrt1.o");

            // darwin_crt2 spec is empty.
          }
        } else {
          if (Args.hasArg(options::OPT_static) ||
              Args.hasArg(options::OPT_object) ||
              Args.hasArg(options::OPT_preload)) {
            CmdArgs.push_back("-lcrt0.o");
          } else {
            // Derived from darwin_crt1 spec.
            if (isMacosxVersionLT(MacosxVersion, 10, 5))
              CmdArgs.push_back("-lcrt1.o");
            else if (isMacosxVersionLT(MacosxVersion, 10, 6))
              CmdArgs.push_back("-lcrt1.10.5.o");
            else
              CmdArgs.push_back("-lcrt1.10.6.o");

            // darwin_crt2 spec is empty.
          }
        }
      }
    }

    if (Args.hasArg(options::OPT_shared_libgcc) &&
        !Args.hasArg(options::OPT_miphoneos_version_min_EQ) &&
        isMacosxVersionLT(MacosxVersion, 10, 5)) {
      const char *Str = getToolChain().GetFilePath(C, "crt3.o").c_str();
      CmdArgs.push_back(Args.MakeArgString(Str));
    }
  }

  Args.AddAllArgs(CmdArgs, options::OPT_L);

  if (Args.hasArg(options::OPT_fopenmp))
    // This is more complicated in gcc...
    CmdArgs.push_back("-lgomp");

  // FIXME: Derive these correctly.
  const char *TCDir = getDarwinToolChain().getToolChainDir().c_str();
  if (getToolChain().getArchName() == "x86_64") {
    CmdArgs.push_back(MakeFormattedString(Args,
                                          llvm::format("-L/usr/lib/gcc/%s/x86_64", TCDir)));
    // Intentionally duplicated for (temporary) gcc bug compatibility.
    CmdArgs.push_back(MakeFormattedString(Args,
                                          llvm::format("-L/usr/lib/gcc/%s/x86_64", TCDir)));
  }
  CmdArgs.push_back(MakeFormattedString(Args,
                                        llvm::format("-L/usr/lib/%s", TCDir)));
  CmdArgs.push_back(MakeFormattedString(Args,
                                        llvm::format("-L/usr/lib/gcc/%s", TCDir)));
  // Intentionally duplicated for (temporary) gcc bug compatibility.
  CmdArgs.push_back(MakeFormattedString(Args,
                                        llvm::format("-L/usr/lib/gcc/%s", TCDir)));
  CmdArgs.push_back(MakeFormattedString(Args,
                                        llvm::format("-L/usr/lib/gcc/%s/../../../%s", TCDir, TCDir)));
  CmdArgs.push_back(MakeFormattedString(Args,
                                        llvm::format("-L/usr/lib/gcc/%s/../../..", TCDir)));

  for (InputInfoList::const_iterator
         it = Inputs.begin(), ie = Inputs.end(); it != ie; ++it) {
    const InputInfo &II = *it;
    if (II.isFilename())
      CmdArgs.push_back(II.getFilename());
    else
      II.getInputArg().renderAsInput(Args, CmdArgs);
  }

  if (LinkingOutput) {
    CmdArgs.push_back("-arch_multiple");
    CmdArgs.push_back("-final_output");
    CmdArgs.push_back(LinkingOutput);
  }

  if (Args.hasArg(options::OPT_fprofile_arcs) ||
      Args.hasArg(options::OPT_fprofile_generate) ||
      Args.hasArg(options::OPT_fcreate_profile) ||
      Args.hasArg(options::OPT_coverage))
    CmdArgs.push_back("-lgcov");

  if (Args.hasArg(options::OPT_fnested_functions))
    CmdArgs.push_back("-allow_stack_execute");

  if (!Args.hasArg(options::OPT_nostdlib) &&
      !Args.hasArg(options::OPT_nodefaultlibs)) {
    // FIXME: g++ is more complicated here, it tries to put -lstdc++
    // before -lm, for example.
    if (getToolChain().getHost().getDriver().CCCIsCXX)
      CmdArgs.push_back("-lstdc++");

    // link_ssp spec is empty.

    // Derived from libgcc and lib specs but refactored.
    if (Args.hasArg(options::OPT_static)) {
      CmdArgs.push_back("-lgcc_static");
    } else {
      if (Args.hasArg(options::OPT_static_libgcc)) {
        CmdArgs.push_back("-lgcc_eh");
      } else if (Args.hasArg(options::OPT_miphoneos_version_min_EQ)) {
        // Derived from darwin_iphoneos_libgcc spec.
        CmdArgs.push_back("-lgcc_s.10.5");
      } else if (Args.hasArg(options::OPT_shared_libgcc) ||
                 Args.hasArg(options::OPT_fexceptions) ||
                 Args.hasArg(options::OPT_fgnu_runtime)) {
        // FIXME: This is probably broken on 10.3?
        if (isMacosxVersionLT(MacosxVersion, 10, 5))
          CmdArgs.push_back("-lgcc_s.10.4");
        else if (isMacosxVersionLT(MacosxVersion, 10, 6))
          CmdArgs.push_back("-lgcc_s.10.5");
      } else {
        if (isMacosxVersionLT(MacosxVersion, 10, 3, 9))
          ; // Do nothing.
        else if (isMacosxVersionLT(MacosxVersion, 10, 5))
          CmdArgs.push_back("-lgcc_s.10.4");
        else if (isMacosxVersionLT(MacosxVersion, 10, 6))
          CmdArgs.push_back("-lgcc_s.10.5");
      }

      if (isMacosxVersionLT(MacosxVersion, 10, 6)) {
        CmdArgs.push_back("-lgcc");
        CmdArgs.push_back("-lSystem");
      } else {
        CmdArgs.push_back("-lSystem");
        CmdArgs.push_back("-lgcc");
      }
    }
  }

  if (!Args.hasArg(options::OPT_A) &&
      !Args.hasArg(options::OPT_nostdlib) &&
      !Args.hasArg(options::OPT_nostartfiles)) {
    // endfile_spec is empty.
  }

  Args.AddAllArgs(CmdArgs, options::OPT_T_Group);
  Args.AddAllArgs(CmdArgs, options::OPT_F);

  const char *Exec =
    Args.MakeArgString(getToolChain().GetProgramPath(C, "collect2").c_str());
  Dest.addCommand(new Command(Exec, CmdArgs));

  // Find the first non-empty base input (we want to ignore linker
  // inputs).
  const char *BaseInput = "";
  for (unsigned i = 0, e = Inputs.size(); i != e; ++i) {
    if (Inputs[i].getBaseInput()[0] != '\0') {
      BaseInput = Inputs[i].getBaseInput();
      break;
    }
  }

  if (Args.getLastArg(options::OPT_g_Group) &&
      !Args.getLastArg(options::OPT_gstabs) &&
      !Args.getLastArg(options::OPT_g0)) {
    // FIXME: This is gross, but matches gcc. The test only considers
    // the suffix (not the -x type), and then only of the first
    // source input. Awesome.
    const char *Suffix = strrchr(BaseInput, '.');
    if (Suffix && isSourceSuffix(Suffix + 1)) {
      const char *Exec =
        Args.MakeArgString(getToolChain().GetProgramPath(C, "dsymutil").c_str());
      ArgStringList CmdArgs;
      CmdArgs.push_back(Output.getFilename());
      C.getJobs().addCommand(new Command(Exec, CmdArgs));
    }
  }
}

void darwin::Lipo::ConstructJob(Compilation &C, const JobAction &JA,
                                Job &Dest, const InputInfo &Output,
                                const InputInfoList &Inputs,
                                const ArgList &Args,
                                const char *LinkingOutput) const {
  ArgStringList CmdArgs;

  CmdArgs.push_back("-create");
  assert(Output.isFilename() && "Unexpected lipo output.");

  CmdArgs.push_back("-output");
  CmdArgs.push_back(Output.getFilename());

  for (InputInfoList::const_iterator
         it = Inputs.begin(), ie = Inputs.end(); it != ie; ++it) {
    const InputInfo &II = *it;
    assert(II.isFilename() && "Unexpected lipo input.");
    CmdArgs.push_back(II.getFilename());
  }
  const char *Exec =
    Args.MakeArgString(getToolChain().GetProgramPath(C, "lipo").c_str());
  Dest.addCommand(new Command(Exec, CmdArgs));
}


void freebsd::Assemble::ConstructJob(Compilation &C, const JobAction &JA,
                                     Job &Dest, const InputInfo &Output,
                                     const InputInfoList &Inputs,
                                     const ArgList &Args,
                                     const char *LinkingOutput) const
{
  ArgStringList CmdArgs;

  // When building 32-bit code on FreeBSD/amd64, we have to explicitly
  // instruct as in the base system to assemble 32-bit code.
  if (getToolChain().getArchName() == "i386")
    CmdArgs.push_back("--32");

  Args.AddAllArgValues(CmdArgs, options::OPT_Wa_COMMA,
                       options::OPT_Xassembler);

  CmdArgs.push_back("-o");
  if (Output.isPipe())
    CmdArgs.push_back("-");
  else
    CmdArgs.push_back(Output.getFilename());

  for (InputInfoList::const_iterator
         it = Inputs.begin(), ie = Inputs.end(); it != ie; ++it) {
    const InputInfo &II = *it;
    if (II.isPipe())
      CmdArgs.push_back("-");
    else
      CmdArgs.push_back(II.getFilename());
  }

  const char *Exec =
    Args.MakeArgString(getToolChain().GetProgramPath(C, "as").c_str());
  Dest.addCommand(new Command(Exec, CmdArgs));
}

void freebsd::Link::ConstructJob(Compilation &C, const JobAction &JA,
                                 Job &Dest, const InputInfo &Output,
                                 const InputInfoList &Inputs,
                                 const ArgList &Args,
                                 const char *LinkingOutput) const
{
  ArgStringList CmdArgs;

  if (Args.hasArg(options::OPT_static)) {
    CmdArgs.push_back("-Bstatic");
  } else {
    CmdArgs.push_back("--eh-frame-hdr");
    if (Args.hasArg(options::OPT_shared)) {
      CmdArgs.push_back("-Bshareable");
    } else {
      CmdArgs.push_back("-dynamic-linker");
      CmdArgs.push_back("/libexec/ld-elf.so.1");
    }
  }

  // When building 32-bit code on FreeBSD/amd64, we have to explicitly
  // instruct ld in the base system to link 32-bit code.
  if (getToolChain().getArchName() == "i386") {
    CmdArgs.push_back("-m");
    CmdArgs.push_back("elf_i386_fbsd");
  }

  if (Output.isPipe()) {
    CmdArgs.push_back("-o");
    CmdArgs.push_back("-");
  } else if (Output.isFilename()) {
    CmdArgs.push_back("-o");
    CmdArgs.push_back(Output.getFilename());
  } else {
    assert(Output.isNothing() && "Invalid output.");
  }

  if (!Args.hasArg(options::OPT_nostdlib) &&
      !Args.hasArg(options::OPT_nostartfiles)) {
    if (!Args.hasArg(options::OPT_shared)) {
      CmdArgs.push_back(Args.MakeArgString(getToolChain().GetFilePath(C, "crt1.o").c_str()));
      CmdArgs.push_back(Args.MakeArgString(getToolChain().GetFilePath(C, "crti.o").c_str()));
      CmdArgs.push_back(Args.MakeArgString(getToolChain().GetFilePath(C, "crtbegin.o").c_str()));
    } else {
      CmdArgs.push_back(Args.MakeArgString(getToolChain().GetFilePath(C, "crti.o").c_str()));
      CmdArgs.push_back(Args.MakeArgString(getToolChain().GetFilePath(C, "crtbeginS.o").c_str()));
    }
  }

  Args.AddAllArgs(CmdArgs, options::OPT_L);
  Args.AddAllArgs(CmdArgs, options::OPT_T_Group);
  Args.AddAllArgs(CmdArgs, options::OPT_e);

  for (InputInfoList::const_iterator
         it = Inputs.begin(), ie = Inputs.end(); it != ie; ++it) {
    const InputInfo &II = *it;
    if (II.isPipe())
      CmdArgs.push_back("-");
    else if (II.isFilename())
      CmdArgs.push_back(II.getFilename());
    else
      II.getInputArg().renderAsInput(Args, CmdArgs);
  }

  if (!Args.hasArg(options::OPT_nostdlib) &&
      !Args.hasArg(options::OPT_nodefaultlibs)) {
    // FIXME: For some reason GCC passes -lgcc and -lgcc_s before adding
    // the default system libraries. Just mimic this for now.
    CmdArgs.push_back("-lgcc");
    if (Args.hasArg(options::OPT_static)) {
      CmdArgs.push_back("-lgcc_eh");
    } else {
      CmdArgs.push_back("--as-needed");
      CmdArgs.push_back("-lgcc_s");
      CmdArgs.push_back("--no-as-needed");
    }

    if (Args.hasArg(options::OPT_pthread))
      CmdArgs.push_back("-lpthread");
    CmdArgs.push_back("-lc");

    CmdArgs.push_back("-lgcc");
    if (Args.hasArg(options::OPT_static)) {
      CmdArgs.push_back("-lgcc_eh");
    } else {
      CmdArgs.push_back("--as-needed");
      CmdArgs.push_back("-lgcc_s");
      CmdArgs.push_back("--no-as-needed");
    }
  }

  if (!Args.hasArg(options::OPT_nostdlib) &&
      !Args.hasArg(options::OPT_nostartfiles)) {
    if (!Args.hasArg(options::OPT_shared))
      CmdArgs.push_back(Args.MakeArgString(getToolChain().GetFilePath(C, "crtend.o").c_str()));
    else
      CmdArgs.push_back(Args.MakeArgString(getToolChain().GetFilePath(C, "crtendS.o").c_str()));
    CmdArgs.push_back(Args.MakeArgString(getToolChain().GetFilePath(C, "crtn.o").c_str()));
  }

  const char *Exec =
    Args.MakeArgString(getToolChain().GetProgramPath(C, "ld").c_str());
  Dest.addCommand(new Command(Exec, CmdArgs));
}