contrib/llvm-project/clang/lib/Driver/ToolChains/WebAssembly.cpp

   1 //===--- WebAssembly.cpp - WebAssembly ToolChain Implementation -*- C++ -*-===//
   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 #include "WebAssembly.h"
  10 #include "CommonArgs.h"
  11 #include "Gnu.h"
  12 #include "clang/Basic/Version.h"
  13 #include "clang/Config/config.h"
  14 #include "clang/Driver/Compilation.h"
  15 #include "clang/Driver/Driver.h"
  16 #include "clang/Driver/DriverDiagnostic.h"
  17 #include "clang/Driver/Options.h"
  18 #include "llvm/Option/ArgList.h"
  19 #include "llvm/Support/FileSystem.h"
  20 #include "llvm/Support/Path.h"
  21 #include "llvm/Support/VirtualFileSystem.h"
  22
  23 using namespace clang::driver;
  24 using namespace clang::driver::tools;
  25 using namespace clang::driver::toolchains;
  26 using namespace clang;
  27 using namespace llvm::opt;
  28
  29 /// Following the conventions in https://wiki.debian.org/Multiarch/Tuples,
  30 /// we remove the vendor field to form the multiarch triple.
  31 std::string WebAssembly::getMultiarchTriple(const Driver &D,
  32                                             const llvm::Triple &TargetTriple,
  33                                             StringRef SysRoot) const {
  34     return (TargetTriple.getArchName() + "-" +
  35             TargetTriple.getOSAndEnvironmentName()).str();
  36 }
  37
  38 std::string wasm::Linker::getLinkerPath(const ArgList &Args) const {
  39   const ToolChain &ToolChain = getToolChain();
  40   if (const Arg* A = Args.getLastArg(options::OPT_fuse_ld_EQ)) {
  41     StringRef UseLinker = A->getValue();
  42     if (!UseLinker.empty()) {
  43       if (llvm::sys::path::is_absolute(UseLinker) &&
  44           llvm::sys::fs::can_execute(UseLinker))
  45         return std::string(UseLinker);
  46
  47       // Accept 'lld', and 'ld' as aliases for the default linker
  48       if (UseLinker != "lld" && UseLinker != "ld")
  49         ToolChain.getDriver().Diag(diag::err_drv_invalid_linker_name)
  50             << A->getAsString(Args);
  51     }
  52   }
  53
  54   return ToolChain.GetProgramPath(ToolChain.getDefaultLinker());
  55 }
  56
  57 void wasm::Linker::ConstructJob(Compilation &C, const JobAction &JA,
  58                                 const InputInfo &Output,
  59                                 const InputInfoList &Inputs,
  60                                 const ArgList &Args,
  61                                 const char *LinkingOutput) const {
  62
  63   const ToolChain &ToolChain = getToolChain();
  64   const char *Linker = Args.MakeArgString(getLinkerPath(Args));
  65   ArgStringList CmdArgs;
  66
  67   CmdArgs.push_back("-m");
  68   if (ToolChain.getTriple().isArch64Bit())
  69     CmdArgs.push_back("wasm64");
  70   else
  71     CmdArgs.push_back("wasm32");
  72
  73   if (Args.hasArg(options::OPT_s))
  74     CmdArgs.push_back("--strip-all");
  75
  76   Args.AddAllArgs(CmdArgs, options::OPT_L);
  77   Args.AddAllArgs(CmdArgs, options::OPT_u);
  78   ToolChain.AddFilePathLibArgs(Args, CmdArgs);
  79
  80   bool IsCommand = true;
  81   const char *Crt1;
  82   const char *Entry = nullptr;
  83
  84   // When -shared is specified, use the reactor exec model unless
  85   // specified otherwise.
  86   if (Args.hasArg(options::OPT_shared))
  87     IsCommand = false;
  88
  89   if (const Arg *A = Args.getLastArg(options::OPT_mexec_model_EQ)) {
  90     StringRef CM = A->getValue();
  91     if (CM == "command") {
  92       IsCommand = true;
  93     } else if (CM == "reactor") {
  94       IsCommand = false;
  95     } else {
  96       ToolChain.getDriver().Diag(diag::err_drv_invalid_argument_to_option)
  97           << CM << A->getOption().getName();
  98     }
  99   }
 100
 101   if (IsCommand) {
 102     // If crt1-command.o exists, it supports new-style commands, so use it.
 103     // Otherwise, use the old crt1.o. This is a temporary transition measure.
 104     // Once WASI libc no longer needs to support LLVM versions which lack
 105     // support for new-style command, it can make crt1.o the same as
 106     // crt1-command.o. And once LLVM no longer needs to support WASI libc
 107     // versions before that, it can switch to using crt1-command.o.
 108     Crt1 = "crt1.o";
 109     if (ToolChain.GetFilePath("crt1-command.o") != "crt1-command.o")
 110       Crt1 = "crt1-command.o";
 111   } else {
 112     Crt1 = "crt1-reactor.o";
 113     Entry = "_initialize";
 114   }
 115
 116   if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nostartfiles))
 117     CmdArgs.push_back(Args.MakeArgString(ToolChain.GetFilePath(Crt1)));
 118   if (Entry) {
 119     CmdArgs.push_back(Args.MakeArgString("--entry"));
 120     CmdArgs.push_back(Args.MakeArgString(Entry));
 121   }
 122
 123   if (Args.hasArg(options::OPT_shared))
 124     CmdArgs.push_back(Args.MakeArgString("-shared"));
 125
 126   AddLinkerInputs(ToolChain, Inputs, Args, CmdArgs, JA);
 127
 128   if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nodefaultlibs)) {
 129     if (ToolChain.ShouldLinkCXXStdlib(Args))
 130       ToolChain.AddCXXStdlibLibArgs(Args, CmdArgs);
 131
 132     if (Args.hasArg(options::OPT_pthread)) {
 133       CmdArgs.push_back("-lpthread");
 134       CmdArgs.push_back("--shared-memory");
 135     }
 136
 137     CmdArgs.push_back("-lc");
 138     AddRunTimeLibs(ToolChain, ToolChain.getDriver(), CmdArgs, Args);
 139   }
 140
 141   CmdArgs.push_back("-o");
 142   CmdArgs.push_back(Output.getFilename());
 143
 144   C.addCommand(std::make_unique<Command>(JA, *this,
 145                                          ResponseFileSupport::AtFileCurCP(),
 146                                          Linker, CmdArgs, Inputs, Output));
 147
 148   // When optimizing, if wasm-opt is available, run it.
 149   if (Arg *A = Args.getLastArg(options::OPT_O_Group)) {
 150     auto WasmOptPath = ToolChain.GetProgramPath("wasm-opt");
 151     if (WasmOptPath != "wasm-opt") {
 152       StringRef OOpt = "s";
 153       if (A->getOption().matches(options::OPT_O4) ||
 154           A->getOption().matches(options::OPT_Ofast))
 155         OOpt = "4";
 156       else if (A->getOption().matches(options::OPT_O0))
 157         OOpt = "0";
 158       else if (A->getOption().matches(options::OPT_O))
 159         OOpt = A->getValue();
 160
 161       if (OOpt != "0") {
 162         const char *WasmOpt = Args.MakeArgString(WasmOptPath);
 163         ArgStringList CmdArgs;
 164         CmdArgs.push_back(Output.getFilename());
 165         CmdArgs.push_back(Args.MakeArgString(llvm::Twine("-O") + OOpt));
 166         CmdArgs.push_back("-o");
 167         CmdArgs.push_back(Output.getFilename());
 168         C.addCommand(std::make_unique<Command>(
 169             JA, *this, ResponseFileSupport::AtFileCurCP(), WasmOpt, CmdArgs,
 170             Inputs, Output));
 171       }
 172     }
 173   }
 174 }
 175
 176 /// Given a base library directory, append path components to form the
 177 /// LTO directory.
 178 static std::string AppendLTOLibDir(const std::string &Dir) {
 179     // The version allows the path to be keyed to the specific version of
 180     // LLVM in used, as the bitcode format is not stable.
 181     return Dir + "/llvm-lto/" LLVM_VERSION_STRING;
 182 }
 183
 184 WebAssembly::WebAssembly(const Driver &D, const llvm::Triple &Triple,
 185                          const llvm::opt::ArgList &Args)
 186     : ToolChain(D, Triple, Args) {
 187
 188   assert(Triple.isArch32Bit() != Triple.isArch64Bit());
 189
 190   getProgramPaths().push_back(getDriver().getInstalledDir());
 191
 192   auto SysRoot = getDriver().SysRoot;
 193   if (getTriple().getOS() == llvm::Triple::UnknownOS) {
 194     // Theoretically an "unknown" OS should mean no standard libraries, however
 195     // it could also mean that a custom set of libraries is in use, so just add
 196     // /lib to the search path. Disable multiarch in this case, to discourage
 197     // paths containing "unknown" from acquiring meanings.
 198     getFilePaths().push_back(SysRoot + "/lib");
 199   } else {
 200     const std::string MultiarchTriple =
 201         getMultiarchTriple(getDriver(), Triple, SysRoot);
 202     if (D.isUsingLTO()) {
 203       // For LTO, enable use of lto-enabled sysroot libraries too, if available.
 204       // Note that the directory is keyed to the LLVM revision, as LLVM's
 205       // bitcode format is not stable.
 206       auto Dir = AppendLTOLibDir(SysRoot + "/lib/" + MultiarchTriple);
 207       getFilePaths().push_back(Dir);
 208     }
 209     getFilePaths().push_back(SysRoot + "/lib/" + MultiarchTriple);
 210   }
 211 }
 212
 213 bool WebAssembly::IsMathErrnoDefault() const { return false; }
 214
 215 bool WebAssembly::IsObjCNonFragileABIDefault() const { return true; }
 216
 217 bool WebAssembly::UseObjCMixedDispatch() const { return true; }
 218
 219 bool WebAssembly::isPICDefault() const { return false; }
 220
 221 bool WebAssembly::isPIEDefault(const llvm::opt::ArgList &Args) const {
 222   return false;
 223 }
 224
 225 bool WebAssembly::isPICDefaultForced() const { return false; }
 226
 227 bool WebAssembly::hasBlocksRuntime() const { return false; }
 228
 229 // TODO: Support profiling.
 230 bool WebAssembly::SupportsProfiling() const { return false; }
 231
 232 bool WebAssembly::HasNativeLLVMSupport() const { return true; }
 233
 234 void WebAssembly::addClangTargetOptions(const ArgList &DriverArgs,
 235                                         ArgStringList &CC1Args,
 236                                         Action::OffloadKind) const {
 237   if (!DriverArgs.hasFlag(clang::driver::options::OPT_fuse_init_array,
 238                           options::OPT_fno_use_init_array, true))
 239     CC1Args.push_back("-fno-use-init-array");
 240
 241   // '-pthread' implies atomics, bulk-memory, mutable-globals, and sign-ext
 242   if (DriverArgs.hasFlag(options::OPT_pthread, options::OPT_no_pthread,
 243                          false)) {
 244     if (DriverArgs.hasFlag(options::OPT_mno_atomics, options::OPT_matomics,
 245                            false))
 246       getDriver().Diag(diag::err_drv_argument_not_allowed_with)
 247           << "-pthread"
 248           << "-mno-atomics";
 249     if (DriverArgs.hasFlag(options::OPT_mno_bulk_memory,
 250                            options::OPT_mbulk_memory, false))
 251       getDriver().Diag(diag::err_drv_argument_not_allowed_with)
 252           << "-pthread"
 253           << "-mno-bulk-memory";
 254     if (DriverArgs.hasFlag(options::OPT_mno_mutable_globals,
 255                            options::OPT_mmutable_globals, false))
 256       getDriver().Diag(diag::err_drv_argument_not_allowed_with)
 257           << "-pthread"
 258           << "-mno-mutable-globals";
 259     if (DriverArgs.hasFlag(options::OPT_mno_sign_ext, options::OPT_msign_ext,
 260                            false))
 261       getDriver().Diag(diag::err_drv_argument_not_allowed_with)
 262           << "-pthread"
 263           << "-mno-sign-ext";
 264     CC1Args.push_back("-target-feature");
 265     CC1Args.push_back("+atomics");
 266     CC1Args.push_back("-target-feature");
 267     CC1Args.push_back("+bulk-memory");
 268     CC1Args.push_back("-target-feature");
 269     CC1Args.push_back("+mutable-globals");
 270     CC1Args.push_back("-target-feature");
 271     CC1Args.push_back("+sign-ext");
 272   }
 273
 274   if (!DriverArgs.hasFlag(options::OPT_mmutable_globals,
 275                           options::OPT_mno_mutable_globals, false)) {
 276     // -fPIC implies +mutable-globals because the PIC ABI used by the linker
 277     // depends on importing and exporting mutable globals.
 278     llvm::Reloc::Model RelocationModel;
 279     unsigned PICLevel;
 280     bool IsPIE;
 281     std::tie(RelocationModel, PICLevel, IsPIE) =
 282         ParsePICArgs(*this, DriverArgs);
 283     if (RelocationModel == llvm::Reloc::PIC_) {
 284       if (DriverArgs.hasFlag(options::OPT_mno_mutable_globals,
 285                              options::OPT_mmutable_globals, false)) {
 286         getDriver().Diag(diag::err_drv_argument_not_allowed_with)
 287             << "-fPIC"
 288             << "-mno-mutable-globals";
 289       }
 290       CC1Args.push_back("-target-feature");
 291       CC1Args.push_back("+mutable-globals");
 292     }
 293   }
 294
 295   if (DriverArgs.getLastArg(options::OPT_fwasm_exceptions)) {
 296     // '-fwasm-exceptions' is not compatible with '-mno-exception-handling'
 297     if (DriverArgs.hasFlag(options::OPT_mno_exception_handing,
 298                            options::OPT_mexception_handing, false))
 299       getDriver().Diag(diag::err_drv_argument_not_allowed_with)
 300           << "-fwasm-exceptions"
 301           << "-mno-exception-handling";
 302     // '-fwasm-exceptions' is not compatible with
 303     // '-mllvm -enable-emscripten-cxx-exceptions'
 304     for (const Arg *A : DriverArgs.filtered(options::OPT_mllvm)) {
 305       if (StringRef(A->getValue(0)) == "-enable-emscripten-cxx-exceptions")
 306         getDriver().Diag(diag::err_drv_argument_not_allowed_with)
 307             << "-fwasm-exceptions"
 308             << "-mllvm -enable-emscripten-cxx-exceptions";
 309     }
 310     // '-fwasm-exceptions' implies exception-handling feature
 311     CC1Args.push_back("-target-feature");
 312     CC1Args.push_back("+exception-handling");
 313     // Backend needs -wasm-enable-eh to enable Wasm EH
 314     CC1Args.push_back("-mllvm");
 315     CC1Args.push_back("-wasm-enable-eh");
 316   }
 317
 318   for (const Arg *A : DriverArgs.filtered(options::OPT_mllvm)) {
 319     StringRef Opt = A->getValue(0);
 320     if (Opt.startswith("-emscripten-cxx-exceptions-allowed")) {
 321       // '-mllvm -emscripten-cxx-exceptions-allowed' should be used with
 322       // '-mllvm -enable-emscripten-cxx-exceptions'
 323       bool EmEHArgExists = false;
 324       for (const Arg *A : DriverArgs.filtered(options::OPT_mllvm)) {
 325         if (StringRef(A->getValue(0)) == "-enable-emscripten-cxx-exceptions") {
 326           EmEHArgExists = true;
 327           break;
 328         }
 329       }
 330       if (!EmEHArgExists)
 331         getDriver().Diag(diag::err_drv_argument_only_allowed_with)
 332             << "-mllvm -emscripten-cxx-exceptions-allowed"
 333             << "-mllvm -enable-emscripten-cxx-exceptions";
 334
 335       // Prevent functions specified in -emscripten-cxx-exceptions-allowed list
 336       // from being inlined before reaching the wasm backend.
 337       StringRef FuncNamesStr = Opt.split('=').second;
 338       SmallVector<StringRef, 4> FuncNames;
 339       FuncNamesStr.split(FuncNames, ',');
 340       for (auto Name : FuncNames) {
 341         CC1Args.push_back("-mllvm");
 342         CC1Args.push_back(DriverArgs.MakeArgString("--force-attribute=" + Name +
 343                                                    ":noinline"));
 344       }
 345     }
 346
 347     if (Opt.startswith("-wasm-enable-sjlj")) {
 348       // '-mllvm -wasm-enable-sjlj' is not compatible with
 349       // '-mno-exception-handling'
 350       if (DriverArgs.hasFlag(options::OPT_mno_exception_handing,
 351                              options::OPT_mexception_handing, false))
 352         getDriver().Diag(diag::err_drv_argument_not_allowed_with)
 353             << "-mllvm -wasm-enable-sjlj"
 354             << "-mno-exception-handling";
 355       // '-mllvm -wasm-enable-sjlj' is not compatible with
 356       // '-mllvm -enable-emscripten-cxx-exceptions'
 357       // because we don't allow Emscripten EH + Wasm SjLj
 358       for (const Arg *A : DriverArgs.filtered(options::OPT_mllvm)) {
 359         if (StringRef(A->getValue(0)) == "-enable-emscripten-cxx-exceptions")
 360           getDriver().Diag(diag::err_drv_argument_not_allowed_with)
 361               << "-mllvm -wasm-enable-sjlj"
 362               << "-mllvm -enable-emscripten-cxx-exceptions";
 363       }
 364       // '-mllvm -wasm-enable-sjlj' is not compatible with
 365       // '-mllvm -enable-emscripten-sjlj'
 366       for (const Arg *A : DriverArgs.filtered(options::OPT_mllvm)) {
 367         if (StringRef(A->getValue(0)) == "-enable-emscripten-sjlj")
 368           getDriver().Diag(diag::err_drv_argument_not_allowed_with)
 369               << "-mllvm -wasm-enable-sjlj"
 370               << "-mllvm -enable-emscripten-sjlj";
 371       }
 372       // '-mllvm -wasm-enable-sjlj' implies exception-handling feature
 373       CC1Args.push_back("-target-feature");
 374       CC1Args.push_back("+exception-handling");
 375       // Backend needs '-exception-model=wasm' to use Wasm EH instructions
 376       CC1Args.push_back("-exception-model=wasm");
 377     }
 378   }
 379 }
 380
 381 ToolChain::RuntimeLibType WebAssembly::GetDefaultRuntimeLibType() const {
 382   return ToolChain::RLT_CompilerRT;
 383 }
 384
 385 ToolChain::CXXStdlibType
 386 WebAssembly::GetCXXStdlibType(const ArgList &Args) const {
 387   if (Arg *A = Args.getLastArg(options::OPT_stdlib_EQ)) {
 388     StringRef Value = A->getValue();
 389     if (Value == "libc++")
 390       return ToolChain::CST_Libcxx;
 391     else if (Value == "libstdc++")
 392       return ToolChain::CST_Libstdcxx;
 393     else
 394       getDriver().Diag(diag::err_drv_invalid_stdlib_name)
 395           << A->getAsString(Args);
 396   }
 397   return ToolChain::CST_Libcxx;
 398 }
 399
 400 void WebAssembly::AddClangSystemIncludeArgs(const ArgList &DriverArgs,
 401                                             ArgStringList &CC1Args) const {
 402   if (DriverArgs.hasArg(clang::driver::options::OPT_nostdinc))
 403     return;
 404
 405   const Driver &D = getDriver();
 406
 407   if (!DriverArgs.hasArg(options::OPT_nobuiltininc)) {
 408     SmallString<128> P(D.ResourceDir);
 409     llvm::sys::path::append(P, "include");
 410     addSystemInclude(DriverArgs, CC1Args, P);
 411   }
 412
 413   if (DriverArgs.hasArg(options::OPT_nostdlibinc))
 414     return;
 415
 416   // Check for configure-time C include directories.
 417   StringRef CIncludeDirs(C_INCLUDE_DIRS);
 418   if (CIncludeDirs != "") {
 419     SmallVector<StringRef, 5> dirs;
 420     CIncludeDirs.split(dirs, ":");
 421     for (StringRef dir : dirs) {
 422       StringRef Prefix =
 423           llvm::sys::path::is_absolute(dir) ? "" : StringRef(D.SysRoot);
 424       addExternCSystemInclude(DriverArgs, CC1Args, Prefix + dir);
 425     }
 426     return;
 427   }
 428
 429   if (getTriple().getOS() != llvm::Triple::UnknownOS) {
 430     const std::string MultiarchTriple =
 431         getMultiarchTriple(D, getTriple(), D.SysRoot);
 432     addSystemInclude(DriverArgs, CC1Args, D.SysRoot + "/include/" + MultiarchTriple);
 433   }
 434   addSystemInclude(DriverArgs, CC1Args, D.SysRoot + "/include");
 435 }
 436
 437 void WebAssembly::AddClangCXXStdlibIncludeArgs(const ArgList &DriverArgs,
 438                                                ArgStringList &CC1Args) const {
 439
 440   if (DriverArgs.hasArg(options::OPT_nostdlibinc, options::OPT_nostdinc,
 441                         options::OPT_nostdincxx))
 442     return;
 443
 444   switch (GetCXXStdlibType(DriverArgs)) {
 445   case ToolChain::CST_Libcxx:
 446     addLibCxxIncludePaths(DriverArgs, CC1Args);
 447     break;
 448   case ToolChain::CST_Libstdcxx:
 449     addLibStdCXXIncludePaths(DriverArgs, CC1Args);
 450     break;
 451   }
 452 }
 453
 454 void WebAssembly::AddCXXStdlibLibArgs(const llvm::opt::ArgList &Args,
 455                                       llvm::opt::ArgStringList &CmdArgs) const {
 456
 457   switch (GetCXXStdlibType(Args)) {
 458   case ToolChain::CST_Libcxx:
 459     CmdArgs.push_back("-lc++");
 460     if (Args.hasArg(options::OPT_fexperimental_library))
 461       CmdArgs.push_back("-lc++experimental");
 462     CmdArgs.push_back("-lc++abi");
 463     break;
 464   case ToolChain::CST_Libstdcxx:
 465     CmdArgs.push_back("-lstdc++");
 466     break;
 467   }
 468 }
 469
 470 SanitizerMask WebAssembly::getSupportedSanitizers() const {
 471   SanitizerMask Res = ToolChain::getSupportedSanitizers();
 472   if (getTriple().isOSEmscripten()) {
 473     Res |= SanitizerKind::Vptr | SanitizerKind::Leak | SanitizerKind::Address;
 474   }
 475   // -fsanitize=function places two words before the function label, which are
 476   // -unsupported.
 477   Res &= ~SanitizerKind::Function;
 478   return Res;
 479 }
 480
 481 Tool *WebAssembly::buildLinker() const {
 482   return new tools::wasm::Linker(*this);
 483 }
 484
 485 void WebAssembly::addLibCxxIncludePaths(
 486     const llvm::opt::ArgList &DriverArgs,
 487     llvm::opt::ArgStringList &CC1Args) const {
 488   const Driver &D = getDriver();
 489   std::string SysRoot = computeSysRoot();
 490   std::string LibPath = SysRoot + "/include";
 491   const std::string MultiarchTriple =
 492       getMultiarchTriple(D, getTriple(), SysRoot);
 493   bool IsKnownOs = (getTriple().getOS() != llvm::Triple::UnknownOS);
 494
 495   std::string Version = detectLibcxxVersion(LibPath);
 496   if (Version.empty())
 497     return;
 498
 499   // First add the per-target include path if the OS is known.
 500   if (IsKnownOs) {
 501     std::string TargetDir = LibPath + "/" + MultiarchTriple + "/c++/" + Version;
 502     addSystemInclude(DriverArgs, CC1Args, TargetDir);
 503   }
 504
 505   // Second add the generic one.
 506   addSystemInclude(DriverArgs, CC1Args, LibPath + "/c++/" + Version);
 507 }
 508
 509 void WebAssembly::addLibStdCXXIncludePaths(
 510     const llvm::opt::ArgList &DriverArgs,
 511     llvm::opt::ArgStringList &CC1Args) const {
 512   // We cannot use GCCInstallationDetector here as the sysroot usually does
 513   // not contain a full GCC installation.
 514   // Instead, we search the given sysroot for /usr/include/xx, similar
 515   // to how we do it for libc++.
 516   const Driver &D = getDriver();
 517   std::string SysRoot = computeSysRoot();
 518   std::string LibPath = SysRoot + "/include";
 519   const std::string MultiarchTriple =
 520       getMultiarchTriple(D, getTriple(), SysRoot);
 521   bool IsKnownOs = (getTriple().getOS() != llvm::Triple::UnknownOS);
 522
 523   // This is similar to detectLibcxxVersion()
 524   std::string Version;
 525   {
 526     std::error_code EC;
 527     Generic_GCC::GCCVersion MaxVersion =
 528         Generic_GCC::GCCVersion::Parse("0.0.0");
 529     SmallString<128> Path(LibPath);
 530     llvm::sys::path::append(Path, "c++");
 531     for (llvm::vfs::directory_iterator LI = getVFS().dir_begin(Path, EC), LE;
 532          !EC && LI != LE; LI = LI.increment(EC)) {
 533       StringRef VersionText = llvm::sys::path::filename(LI->path());
 534       if (VersionText[0] != 'v') {
 535         auto Version = Generic_GCC::GCCVersion::Parse(VersionText);
 536         if (Version > MaxVersion)
 537           MaxVersion = Version;
 538       }
 539     }
 540     if (MaxVersion.Major > 0)
 541       Version = MaxVersion.Text;
 542   }
 543
 544   if (Version.empty())
 545     return;
 546
 547   // First add the per-target include path if the OS is known.
 548   if (IsKnownOs) {
 549     std::string TargetDir = LibPath + "/c++/" + Version + "/" + MultiarchTriple;
 550     addSystemInclude(DriverArgs, CC1Args, TargetDir);
 551   }
 552
 553   // Second add the generic one.
 554   addSystemInclude(DriverArgs, CC1Args, LibPath + "/c++/" + Version);
 555   // Third the backward one.
 556   addSystemInclude(DriverArgs, CC1Args, LibPath + "/c++/" + Version + "/backward");
 557 }