vendor/clang/clang-trunk-r300422

1 files changed, 1421 insertions, 0 deletions

diff --git a/lib/Driver/ToolChains/MSVC.cpp b/lib/Driver/ToolChains/MSVC.cpp
new file mode 100644
index 0000000000000..a09304814ca69
--- /dev/null
+++ b/lib/Driver/ToolChains/MSVC.cpp
@@ -0,0 +1,1421 @@
+//===--- ToolChains.cpp - ToolChain Implementations -----------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "MSVC.h"
+#include "CommonArgs.h"
+#include "Darwin.h"
+#include "clang/Basic/CharInfo.h"
+#include "clang/Basic/Version.h"
+#include "clang/Driver/Compilation.h"
+#include "clang/Driver/Driver.h"
+#include "clang/Driver/DriverDiagnostic.h"
+#include "clang/Driver/Options.h"
+#include "clang/Driver/SanitizerArgs.h"
+#include "llvm/ADT/StringExtras.h"
+#include "llvm/ADT/StringSwitch.h"
+#include "llvm/Config/llvm-config.h"
+#include "llvm/Option/Arg.h"
+#include "llvm/Option/ArgList.h"
+#include "llvm/Support/ConvertUTF.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/FileSystem.h"
+#include "llvm/Support/Host.h"
+#include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Support/Path.h"
+#include "llvm/Support/Process.h"
+#include <cstdio>
+
+// Include the necessary headers to interface with the Windows registry and
+// environment.
+#if defined(LLVM_ON_WIN32)
+#define USE_WIN32
+#endif
+
+#ifdef USE_WIN32
+  #define WIN32_LEAN_AND_MEAN
+  #define NOGDI
+  #ifndef NOMINMAX
+    #define NOMINMAX
+  #endif
+  #include <windows.h>
+#endif
+
+#ifdef _MSC_VER
+// Don't support SetupApi on MinGW.
+#define USE_MSVC_SETUP_API
+
+// Make sure this comes before MSVCSetupApi.h
+#include <comdef.h>
+
+#include "MSVCSetupApi.h"
+#include "llvm/Support/COM.h"
+_COM_SMARTPTR_TYPEDEF(ISetupConfiguration, __uuidof(ISetupConfiguration));
+_COM_SMARTPTR_TYPEDEF(ISetupConfiguration2, __uuidof(ISetupConfiguration2));
+_COM_SMARTPTR_TYPEDEF(ISetupHelper, __uuidof(ISetupHelper));
+_COM_SMARTPTR_TYPEDEF(IEnumSetupInstances, __uuidof(IEnumSetupInstances));
+_COM_SMARTPTR_TYPEDEF(ISetupInstance, __uuidof(ISetupInstance));
+_COM_SMARTPTR_TYPEDEF(ISetupInstance2, __uuidof(ISetupInstance2));
+#endif
+
+using namespace clang::driver;
+using namespace clang::driver::toolchains;
+using namespace clang::driver::tools;
+using namespace clang;
+using namespace llvm::opt;
+
+// Defined below.
+// Forward declare this so there aren't too many things above the constructor.
+static bool getSystemRegistryString(const char *keyPath, const char *valueName,
+                                    std::string &value, std::string *phValue);
+
+// Check various environment variables to try and find a toolchain.
+static bool findVCToolChainViaEnvironment(std::string &Path,
+                                          bool &IsVS2017OrNewer) {
+  // These variables are typically set by vcvarsall.bat
+  // when launching a developer command prompt.
+  if (llvm::Optional<std::string> VCToolsInstallDir =
+          llvm::sys::Process::GetEnv("VCToolsInstallDir")) {
+    // This is only set by newer Visual Studios, and it leads straight to
+    // the toolchain directory.
+    Path = std::move(*VCToolsInstallDir);
+    IsVS2017OrNewer = true;
+    return true;
+  }
+  if (llvm::Optional<std::string> VCInstallDir =
+          llvm::sys::Process::GetEnv("VCINSTALLDIR")) {
+    // If the previous variable isn't set but this one is, then we've found
+    // an older Visual Studio. This variable is set by newer Visual Studios too,
+    // so this check has to appear second.
+    // In older Visual Studios, the VC directory is the toolchain.
+    Path = std::move(*VCInstallDir);
+    IsVS2017OrNewer = false;
+    return true;
+  }
+
+  // We couldn't find any VC environment variables. Let's walk through PATH and
+  // see if it leads us to a VC toolchain bin directory. If it does, pick the
+  // first one that we find.
+  if (llvm::Optional<std::string> PathEnv =
+          llvm::sys::Process::GetEnv("PATH")) {
+    llvm::SmallVector<llvm::StringRef, 8> PathEntries;
+    llvm::StringRef(*PathEnv).split(PathEntries, llvm::sys::EnvPathSeparator);
+    for (llvm::StringRef PathEntry : PathEntries) {
+      if (PathEntry.empty())
+        continue;
+
+      llvm::SmallString<256> ExeTestPath;
+
+      // If cl.exe doesn't exist, then this definitely isn't a VC toolchain.
+      ExeTestPath = PathEntry;
+      llvm::sys::path::append(ExeTestPath, "cl.exe");
+      if (!llvm::sys::fs::exists(ExeTestPath))
+        continue;
+
+      // cl.exe existing isn't a conclusive test for a VC toolchain; clang also
+      // has a cl.exe. So let's check for link.exe too.
+      ExeTestPath = PathEntry;
+      llvm::sys::path::append(ExeTestPath, "link.exe");
+      if (!llvm::sys::fs::exists(ExeTestPath))
+        continue;
+
+      // whatever/VC/bin --> old toolchain, VC dir is toolchain dir.
+      if (llvm::sys::path::filename(PathEntry) == "bin") {
+        llvm::StringRef ParentPath = llvm::sys::path::parent_path(PathEntry);
+        if (llvm::sys::path::filename(ParentPath) == "VC") {
+          Path = ParentPath;
+          IsVS2017OrNewer = false;
+          return true;
+        }
+
+      } else {
+        // This could be a new (>=VS2017) toolchain. If it is, we should find
+        // path components with these prefixes when walking backwards through
+        // the path.
+        // Note: empty strings match anything.
+        llvm::StringRef ExpectedPrefixes[] = {"",     "Host",  "bin", "",
+                                              "MSVC", "Tools", "VC"};
+
+        auto It = llvm::sys::path::rbegin(PathEntry);
+        auto End = llvm::sys::path::rend(PathEntry);
+        for (llvm::StringRef Prefix : ExpectedPrefixes) {
+          if (It == End)
+            goto NotAToolChain;
+          if (!It->startswith(Prefix))
+            goto NotAToolChain;
+          ++It;
+        }
+
+        // We've found a new toolchain!
+        // Back up 3 times (/bin/Host/arch) to get the root path.
+        llvm::StringRef ToolChainPath(PathEntry);
+        for (int i = 0; i < 3; ++i)
+          ToolChainPath = llvm::sys::path::parent_path(ToolChainPath);
+
+        Path = ToolChainPath;
+        IsVS2017OrNewer = true;
+        return true;
+      }
+
+    NotAToolChain:
+      continue;
+    }
+  }
+  return false;
+}
+
+// Query the Setup Config server for installs, then pick the newest version
+// and find its default VC toolchain.
+// This is the preferred way to discover new Visual Studios, as they're no
+// longer listed in the registry.
+static bool findVCToolChainViaSetupConfig(std::string &Path,
+                                          bool &IsVS2017OrNewer) {
+#if !defined(USE_MSVC_SETUP_API)
+  return false;
+#else
+  // FIXME: This really should be done once in the top-level program's main
+  // function, as it may have already been initialized with a different
+  // threading model otherwise.
+  llvm::sys::InitializeCOMRAII COM(llvm::sys::COMThreadingMode::SingleThreaded);
+  HRESULT HR;
+
+  // _com_ptr_t will throw a _com_error if a COM calls fail.
+  // The LLVM coding standards forbid exception handling, so we'll have to
+  // stop them from being thrown in the first place.
+  // The destructor will put the regular error handler back when we leave
+  // this scope.
+  struct SuppressCOMErrorsRAII {
+    static void __stdcall handler(HRESULT hr, IErrorInfo *perrinfo) {}
+
+    SuppressCOMErrorsRAII() { _set_com_error_handler(handler); }
+
+    ~SuppressCOMErrorsRAII() { _set_com_error_handler(_com_raise_error); }
+
+  } COMErrorSuppressor;
+
+  ISetupConfigurationPtr Query;
+  HR = Query.CreateInstance(__uuidof(SetupConfiguration));
+  if (FAILED(HR))
+    return false;
+
+  IEnumSetupInstancesPtr EnumInstances;
+  HR = ISetupConfiguration2Ptr(Query)->EnumAllInstances(&EnumInstances);
+  if (FAILED(HR))
+    return false;
+
+  ISetupInstancePtr Instance;
+  HR = EnumInstances->Next(1, &Instance, nullptr);
+  if (HR != S_OK)
+    return false;
+
+  ISetupInstancePtr NewestInstance;
+  Optional<uint64_t> NewestVersionNum;
+  do {
+    bstr_t VersionString;
+    uint64_t VersionNum;
+    HR = Instance->GetInstallationVersion(VersionString.GetAddress());
+    if (FAILED(HR))
+      continue;
+    HR = ISetupHelperPtr(Query)->ParseVersion(VersionString, &VersionNum);
+    if (FAILED(HR))
+      continue;
+    if (!NewestVersionNum || (VersionNum > NewestVersionNum)) {
+      NewestInstance = Instance;
+      NewestVersionNum = VersionNum;
+    }
+  } while ((HR = EnumInstances->Next(1, &Instance, nullptr)) == S_OK);
+
+  if (!NewestInstance)
+    return false;
+
+  bstr_t VCPathWide;
+  HR = NewestInstance->ResolvePath(L"VC", VCPathWide.GetAddress());
+  if (FAILED(HR))
+    return false;
+
+  std::string VCRootPath;
+  llvm::convertWideToUTF8(std::wstring(VCPathWide), VCRootPath);
+
+  llvm::SmallString<256> ToolsVersionFilePath(VCRootPath);
+  llvm::sys::path::append(ToolsVersionFilePath, "Auxiliary", "Build",
+                          "Microsoft.VCToolsVersion.default.txt");
+
+  auto ToolsVersionFile = llvm::MemoryBuffer::getFile(ToolsVersionFilePath);
+  if (!ToolsVersionFile)
+    return false;
+
+  llvm::SmallString<256> ToolchainPath(VCRootPath);
+  llvm::sys::path::append(ToolchainPath, "Tools", "MSVC",
+                          ToolsVersionFile->get()->getBuffer().rtrim());
+  if (!llvm::sys::fs::is_directory(ToolchainPath))
+    return false;
+
+  Path = ToolchainPath.str();
+  IsVS2017OrNewer = true;
+  return true;
+#endif
+}
+
+// Look in the registry for Visual Studio installs, and use that to get
+// a toolchain path. VS2017 and newer don't get added to the registry.
+// So if we find something here, we know that it's an older version.
+static bool findVCToolChainViaRegistry(std::string &Path,
+                                       bool &IsVS2017OrNewer) {
+  std::string VSInstallPath;
+  if (getSystemRegistryString(R"(SOFTWARE\Microsoft\VisualStudio\$VERSION)",
+                              "InstallDir", VSInstallPath, nullptr) ||
+      getSystemRegistryString(R"(SOFTWARE\Microsoft\VCExpress\$VERSION)",
+                              "InstallDir", VSInstallPath, nullptr)) {
+    if (!VSInstallPath.empty()) {
+      llvm::SmallString<256> VCPath(llvm::StringRef(
+          VSInstallPath.c_str(), VSInstallPath.find(R"(\Common7\IDE)")));
+      llvm::sys::path::append(VCPath, "VC");
+
+      Path = VCPath.str();
+      IsVS2017OrNewer = false;
+      return true;
+    }
+  }
+  return false;
+}
+
+// Try to find Exe from a Visual Studio distribution.  This first tries to find
+// an installed copy of Visual Studio and, failing that, looks in the PATH,
+// making sure that whatever executable that's found is not a same-named exe
+// from clang itself to prevent clang from falling back to itself.
+static std::string FindVisualStudioExecutable(const ToolChain &TC,
+                                              const char *Exe) {
+  const auto &MSVC = static_cast<const toolchains::MSVCToolChain &>(TC);
+  SmallString<128> FilePath(MSVC.getSubDirectoryPath(
+      toolchains::MSVCToolChain::SubDirectoryType::Bin));
+  llvm::sys::path::append(FilePath, Exe);
+  return llvm::sys::fs::can_execute(FilePath) ? FilePath.str() : Exe;
+}
+
+void visualstudio::Linker::ConstructJob(Compilation &C, const JobAction &JA,
+                                        const InputInfo &Output,
+                                        const InputInfoList &Inputs,
+                                        const ArgList &Args,
+                                        const char *LinkingOutput) const {
+  ArgStringList CmdArgs;
+
+  auto &TC = static_cast<const toolchains::MSVCToolChain &>(getToolChain());
+
+  assert((Output.isFilename() || Output.isNothing()) && "invalid output");
+  if (Output.isFilename())
+    CmdArgs.push_back(
+        Args.MakeArgString(std::string("-out:") + Output.getFilename()));
+
+  if (!Args.hasArg(options::OPT_nostdlib, options::OPT_nostartfiles) &&
+      !C.getDriver().IsCLMode())
+    CmdArgs.push_back("-defaultlib:libcmt");
+
+  if (!llvm::sys::Process::GetEnv("LIB")) {
+    // If the VC environment hasn't been configured (perhaps because the user
+    // did not run vcvarsall), try to build a consistent link environment.  If
+    // the environment variable is set however, assume the user knows what
+    // they're doing.
+    CmdArgs.push_back(Args.MakeArgString(
+        Twine("-libpath:") +
+        TC.getSubDirectoryPath(
+            toolchains::MSVCToolChain::SubDirectoryType::Lib)));
+
+    if (TC.useUniversalCRT()) {
+      std::string UniversalCRTLibPath;
+      if (TC.getUniversalCRTLibraryPath(UniversalCRTLibPath))
+        CmdArgs.push_back(
+            Args.MakeArgString(Twine("-libpath:") + UniversalCRTLibPath));
+    }
+
+    std::string WindowsSdkLibPath;
+    if (TC.getWindowsSDKLibraryPath(WindowsSdkLibPath))
+      CmdArgs.push_back(
+          Args.MakeArgString(std::string("-libpath:") + WindowsSdkLibPath));
+  }
+
+  if (!C.getDriver().IsCLMode() && Args.hasArg(options::OPT_L))
+    for (const auto &LibPath : Args.getAllArgValues(options::OPT_L))
+      CmdArgs.push_back(Args.MakeArgString("-libpath:" + LibPath));
+
+  CmdArgs.push_back("-nologo");
+
+  if (Args.hasArg(options::OPT_g_Group, options::OPT__SLASH_Z7,
+                  options::OPT__SLASH_Zd))
+    CmdArgs.push_back("-debug");
+
+  bool DLL = Args.hasArg(options::OPT__SLASH_LD, options::OPT__SLASH_LDd,
+                         options::OPT_shared);
+  if (DLL) {
+    CmdArgs.push_back(Args.MakeArgString("-dll"));
+
+    SmallString<128> ImplibName(Output.getFilename());
+    llvm::sys::path::replace_extension(ImplibName, "lib");
+    CmdArgs.push_back(Args.MakeArgString(std::string("-implib:") + ImplibName));
+  }
+
+  if (TC.getSanitizerArgs().needsAsanRt()) {
+    CmdArgs.push_back(Args.MakeArgString("-debug"));
+    CmdArgs.push_back(Args.MakeArgString("-incremental:no"));
+    if (TC.getSanitizerArgs().needsSharedAsanRt() ||
+        Args.hasArg(options::OPT__SLASH_MD, options::OPT__SLASH_MDd)) {
+      for (const auto &Lib : {"asan_dynamic", "asan_dynamic_runtime_thunk"})
+        CmdArgs.push_back(TC.getCompilerRTArgString(Args, Lib));
+      // Make sure the dynamic runtime thunk is not optimized out at link time
+      // to ensure proper SEH handling.
+      CmdArgs.push_back(Args.MakeArgString(
+          TC.getArch() == llvm::Triple::x86
+              ? "-include:___asan_seh_interceptor"
+              : "-include:__asan_seh_interceptor"));
+      // Make sure the linker consider all object files from the dynamic runtime
+      // thunk.
+      CmdArgs.push_back(Args.MakeArgString(std::string("-wholearchive:") +
+          TC.getCompilerRT(Args, "asan_dynamic_runtime_thunk")));
+    } else if (DLL) {
+      CmdArgs.push_back(TC.getCompilerRTArgString(Args, "asan_dll_thunk"));
+    } else {
+      for (const auto &Lib : {"asan", "asan_cxx"}) {
+        CmdArgs.push_back(TC.getCompilerRTArgString(Args, Lib));
+        // Make sure the linker consider all object files from the static lib.
+        // This is necessary because instrumented dlls need access to all the
+        // interface exported by the static lib in the main executable.
+        CmdArgs.push_back(Args.MakeArgString(std::string("-wholearchive:") +
+            TC.getCompilerRT(Args, Lib)));
+      }
+    }
+  }
+
+  Args.AddAllArgValues(CmdArgs, options::OPT__SLASH_link);
+
+  if (Args.hasFlag(options::OPT_fopenmp, options::OPT_fopenmp_EQ,
+                   options::OPT_fno_openmp, false)) {
+    CmdArgs.push_back("-nodefaultlib:vcomp.lib");
+    CmdArgs.push_back("-nodefaultlib:vcompd.lib");
+    CmdArgs.push_back(Args.MakeArgString(std::string("-libpath:") +
+                                         TC.getDriver().Dir + "/../lib"));
+    switch (TC.getDriver().getOpenMPRuntime(Args)) {
+    case Driver::OMPRT_OMP:
+      CmdArgs.push_back("-defaultlib:libomp.lib");
+      break;
+    case Driver::OMPRT_IOMP5:
+      CmdArgs.push_back("-defaultlib:libiomp5md.lib");
+      break;
+    case Driver::OMPRT_GOMP:
+      break;
+    case Driver::OMPRT_Unknown:
+      // Already diagnosed.
+      break;
+    }
+  }
+
+  // Add compiler-rt lib in case if it was explicitly
+  // specified as an argument for --rtlib option.
+  if (!Args.hasArg(options::OPT_nostdlib)) {
+    AddRunTimeLibs(TC, TC.getDriver(), CmdArgs, Args);
+  }
+
+  // Add filenames, libraries, and other linker inputs.
+  for (const auto &Input : Inputs) {
+    if (Input.isFilename()) {
+      CmdArgs.push_back(Input.getFilename());
+      continue;
+    }
+
+    const Arg &A = Input.getInputArg();
+
+    // Render -l options differently for the MSVC linker.
+    if (A.getOption().matches(options::OPT_l)) {
+      StringRef Lib = A.getValue();
+      const char *LinkLibArg;
+      if (Lib.endswith(".lib"))
+        LinkLibArg = Args.MakeArgString(Lib);
+      else
+        LinkLibArg = Args.MakeArgString(Lib + ".lib");
+      CmdArgs.push_back(LinkLibArg);
+      continue;
+    }
+
+    // Otherwise, this is some other kind of linker input option like -Wl, -z,
+    // or -L. Render it, even if MSVC doesn't understand it.
+    A.renderAsInput(Args, CmdArgs);
+  }
+
+  TC.addProfileRTLibs(Args, CmdArgs);
+
+  std::vector<const char *> Environment;
+
+  // We need to special case some linker paths.  In the case of lld, we need to
+  // translate 'lld' into 'lld-link', and in the case of the regular msvc
+  // linker, we need to use a special search algorithm.
+  llvm::SmallString<128> linkPath;
+  StringRef Linker = Args.getLastArgValue(options::OPT_fuse_ld_EQ, "link");
+  if (Linker.equals_lower("lld"))
+    Linker = "lld-link";
+
+  if (Linker.equals_lower("link")) {
+    // If we're using the MSVC linker, it's not sufficient to just use link
+    // from the program PATH, because other environments like GnuWin32 install
+    // their own link.exe which may come first.
+    linkPath = FindVisualStudioExecutable(TC, "link.exe");
+
+#ifdef USE_WIN32
+    // When cross-compiling with VS2017 or newer, link.exe expects to have
+    // its containing bin directory at the top of PATH, followed by the
+    // native target bin directory.
+    // e.g. when compiling for x86 on an x64 host, PATH should start with:
+    // /bin/HostX64/x86;/bin/HostX64/x64
+    if (TC.getIsVS2017OrNewer() &&
+        llvm::Triple(llvm::sys::getProcessTriple()).getArch() != TC.getArch()) {
+      auto HostArch = llvm::Triple(llvm::sys::getProcessTriple()).getArch();
+
+      auto EnvBlockWide =
+          std::unique_ptr<wchar_t[], decltype(&FreeEnvironmentStringsW)>(
+              GetEnvironmentStringsW(), FreeEnvironmentStringsW);
+      if (!EnvBlockWide)
+        goto SkipSettingEnvironment;
+
+      size_t EnvCount = 0;
+      size_t EnvBlockLen = 0;
+      while (EnvBlockWide[EnvBlockLen] != L'\0') {
+        ++EnvCount;
+        EnvBlockLen += std::wcslen(&EnvBlockWide[EnvBlockLen]) +
+                       1 /*string null-terminator*/;
+      }
+      ++EnvBlockLen; // add the block null-terminator
+
+      std::string EnvBlock;
+      if (!llvm::convertUTF16ToUTF8String(
+              llvm::ArrayRef<char>(reinterpret_cast<char *>(EnvBlockWide.get()),
+                                   EnvBlockLen * sizeof(EnvBlockWide[0])),
+              EnvBlock))
+        goto SkipSettingEnvironment;
+
+      Environment.reserve(EnvCount);
+
+      // Now loop over each string in the block and copy them into the
+      // environment vector, adjusting the PATH variable as needed when we
+      // find it.
+      for (const char *Cursor = EnvBlock.data(); *Cursor != '\0';) {
+        llvm::StringRef EnvVar(Cursor);
+        if (EnvVar.startswith_lower("path=")) {
+          using SubDirectoryType = toolchains::MSVCToolChain::SubDirectoryType;
+          constexpr size_t PrefixLen = 5; // strlen("path=")
+          Environment.push_back(Args.MakeArgString(
+              EnvVar.substr(0, PrefixLen) +
+              TC.getSubDirectoryPath(SubDirectoryType::Bin) +
+              llvm::Twine(llvm::sys::EnvPathSeparator) +
+              TC.getSubDirectoryPath(SubDirectoryType::Bin, HostArch) +
+              (EnvVar.size() > PrefixLen
+                   ? llvm::Twine(llvm::sys::EnvPathSeparator) +
+                         EnvVar.substr(PrefixLen)
+                   : "")));
+        } else {
+          Environment.push_back(Args.MakeArgString(EnvVar));
+        }
+        Cursor += EnvVar.size() + 1 /*null-terminator*/;
+      }
+    }
+  SkipSettingEnvironment:;
+#endif
+  } else {
+    linkPath = Linker;
+    llvm::sys::path::replace_extension(linkPath, "exe");
+    linkPath = TC.GetProgramPath(linkPath.c_str());
+  }
+
+  auto LinkCmd = llvm::make_unique<Command>(
+      JA, *this, Args.MakeArgString(linkPath), CmdArgs, Inputs);
+  if (!Environment.empty())
+    LinkCmd->setEnvironment(Environment);
+  C.addCommand(std::move(LinkCmd));
+}
+
+void visualstudio::Compiler::ConstructJob(Compilation &C, const JobAction &JA,
+                                          const InputInfo &Output,
+                                          const InputInfoList &Inputs,
+                                          const ArgList &Args,
+                                          const char *LinkingOutput) const {
+  C.addCommand(GetCommand(C, JA, Output, Inputs, Args, LinkingOutput));
+}
+
+std::unique_ptr<Command> visualstudio::Compiler::GetCommand(
+    Compilation &C, const JobAction &JA, const InputInfo &Output,
+    const InputInfoList &Inputs, const ArgList &Args,
+    const char *LinkingOutput) const {
+  ArgStringList CmdArgs;
+  CmdArgs.push_back("/nologo");
+  CmdArgs.push_back("/c");  // Compile only.
+  CmdArgs.push_back("/W0"); // No warnings.
+
+  // The goal is to be able to invoke this tool correctly based on
+  // any flag accepted by clang-cl.
+
+  // These are spelled the same way in clang and cl.exe,.
+  Args.AddAllArgs(CmdArgs, {options::OPT_D, options::OPT_U, options::OPT_I});
+
+  // Optimization level.
+  if (Arg *A = Args.getLastArg(options::OPT_fbuiltin, options::OPT_fno_builtin))
+    CmdArgs.push_back(A->getOption().getID() == options::OPT_fbuiltin ? "/Oi"
+                                                                      : "/Oi-");
+  if (Arg *A = Args.getLastArg(options::OPT_O, options::OPT_O0)) {
+    if (A->getOption().getID() == options::OPT_O0) {
+      CmdArgs.push_back("/Od");
+    } else {
+      CmdArgs.push_back("/Og");
+
+      StringRef OptLevel = A->getValue();
+      if (OptLevel == "s" || OptLevel == "z")
+        CmdArgs.push_back("/Os");
+      else
+        CmdArgs.push_back("/Ot");
+
+      CmdArgs.push_back("/Ob2");
+    }
+  }
+  if (Arg *A = Args.getLastArg(options::OPT_fomit_frame_pointer,
+                               options::OPT_fno_omit_frame_pointer))
+    CmdArgs.push_back(A->getOption().getID() == options::OPT_fomit_frame_pointer
+                          ? "/Oy"
+                          : "/Oy-");
+  if (!Args.hasArg(options::OPT_fwritable_strings))
+    CmdArgs.push_back("/GF");
+
+  // Flags for which clang-cl has an alias.
+  // FIXME: How can we ensure this stays in sync with relevant clang-cl options?
+
+  if (Args.hasFlag(options::OPT__SLASH_GR_, options::OPT__SLASH_GR,
+                   /*default=*/false))
+    CmdArgs.push_back("/GR-");
+
+  if (Args.hasFlag(options::OPT__SLASH_GS_, options::OPT__SLASH_GS,
+                   /*default=*/false))
+    CmdArgs.push_back("/GS-");
+
+  if (Arg *A = Args.getLastArg(options::OPT_ffunction_sections,
+                               options::OPT_fno_function_sections))
+    CmdArgs.push_back(A->getOption().getID() == options::OPT_ffunction_sections
+                          ? "/Gy"
+                          : "/Gy-");
+  if (Arg *A = Args.getLastArg(options::OPT_fdata_sections,
+                               options::OPT_fno_data_sections))
+    CmdArgs.push_back(
+        A->getOption().getID() == options::OPT_fdata_sections ? "/Gw" : "/Gw-");
+  if (Args.hasArg(options::OPT_fsyntax_only))
+    CmdArgs.push_back("/Zs");
+  if (Args.hasArg(options::OPT_g_Flag, options::OPT_gline_tables_only,
+                  options::OPT__SLASH_Z7))
+    CmdArgs.push_back("/Z7");
+
+  std::vector<std::string> Includes =
+      Args.getAllArgValues(options::OPT_include);
+  for (const auto &Include : Includes)
+    CmdArgs.push_back(Args.MakeArgString(std::string("/FI") + Include));
+
+  // Flags that can simply be passed through.
+  Args.AddAllArgs(CmdArgs, options::OPT__SLASH_LD);
+  Args.AddAllArgs(CmdArgs, options::OPT__SLASH_LDd);
+  Args.AddAllArgs(CmdArgs, options::OPT__SLASH_GX);
+  Args.AddAllArgs(CmdArgs, options::OPT__SLASH_GX_);
+  Args.AddAllArgs(CmdArgs, options::OPT__SLASH_EH);
+  Args.AddAllArgs(CmdArgs, options::OPT__SLASH_Zl);
+
+  // The order of these flags is relevant, so pick the last one.
+  if (Arg *A = Args.getLastArg(options::OPT__SLASH_MD, options::OPT__SLASH_MDd,
+                               options::OPT__SLASH_MT, options::OPT__SLASH_MTd))
+    A->render(Args, CmdArgs);
+
+  // Use MSVC's default threadsafe statics behaviour unless there was a flag.
+  if (Arg *A = Args.getLastArg(options::OPT_fthreadsafe_statics,
+                               options::OPT_fno_threadsafe_statics)) {
+    CmdArgs.push_back(A->getOption().getID() == options::OPT_fthreadsafe_statics
+                          ? "/Zc:threadSafeInit"
+                          : "/Zc:threadSafeInit-");
+  }
+
+  // Pass through all unknown arguments so that the fallback command can see
+  // them too.
+  Args.AddAllArgs(CmdArgs, options::OPT_UNKNOWN);
+
+  // Input filename.
+  assert(Inputs.size() == 1);
+  const InputInfo &II = Inputs[0];
+  assert(II.getType() == types::TY_C || II.getType() == types::TY_CXX);
+  CmdArgs.push_back(II.getType() == types::TY_C ? "/Tc" : "/Tp");
+  if (II.isFilename())
+    CmdArgs.push_back(II.getFilename());
+  else
+    II.getInputArg().renderAsInput(Args, CmdArgs);
+
+  // Output filename.
+  assert(Output.getType() == types::TY_Object);
+  const char *Fo =
+      Args.MakeArgString(std::string("/Fo") + Output.getFilename());
+  CmdArgs.push_back(Fo);
+
+  std::string Exec = FindVisualStudioExecutable(getToolChain(), "cl.exe");
+  return llvm::make_unique<Command>(JA, *this, Args.MakeArgString(Exec),
+                                    CmdArgs, Inputs);
+}
+
+MSVCToolChain::MSVCToolChain(const Driver &D, const llvm::Triple &Triple,
+                             const ArgList &Args)
+    : ToolChain(D, Triple, Args), CudaInstallation(D, Triple, Args) {
+  getProgramPaths().push_back(getDriver().getInstalledDir());
+  if (getDriver().getInstalledDir() != getDriver().Dir)
+    getProgramPaths().push_back(getDriver().Dir);
+
+  // Check the environment first, since that's probably the user telling us
+  // what they want to use.
+  // Failing that, just try to find the newest Visual Studio version we can
+  // and use its default VC toolchain.
+  findVCToolChainViaEnvironment(VCToolChainPath, IsVS2017OrNewer) ||
+      findVCToolChainViaSetupConfig(VCToolChainPath, IsVS2017OrNewer) ||
+      findVCToolChainViaRegistry(VCToolChainPath, IsVS2017OrNewer);
+}
+
+Tool *MSVCToolChain::buildLinker() const {
+  if (VCToolChainPath.empty())
+    getDriver().Diag(clang::diag::warn_drv_msvc_not_found);
+  return new tools::visualstudio::Linker(*this);
+}
+
+Tool *MSVCToolChain::buildAssembler() const {
+  if (getTriple().isOSBinFormatMachO())
+    return new tools::darwin::Assembler(*this);
+  getDriver().Diag(clang::diag::err_no_external_assembler);
+  return nullptr;
+}
+
+bool MSVCToolChain::IsIntegratedAssemblerDefault() const {
+  return true;
+}
+
+bool MSVCToolChain::IsUnwindTablesDefault() const {
+  // Emit unwind tables by default on Win64. All non-x86_32 Windows platforms
+  // such as ARM and PPC actually require unwind tables, but LLVM doesn't know
+  // how to generate them yet.
+
+  // Don't emit unwind tables by default for MachO targets.
+  if (getTriple().isOSBinFormatMachO())
+    return false;
+
+  return getArch() == llvm::Triple::x86_64;
+}
+
+bool MSVCToolChain::isPICDefault() const {
+  return getArch() == llvm::Triple::x86_64;
+}
+
+bool MSVCToolChain::isPIEDefault() const {
+  return false;
+}
+
+bool MSVCToolChain::isPICDefaultForced() const {
+  return getArch() == llvm::Triple::x86_64;
+}
+
+void MSVCToolChain::AddCudaIncludeArgs(const ArgList &DriverArgs,
+                                       ArgStringList &CC1Args) const {
+  CudaInstallation.AddCudaIncludeArgs(DriverArgs, CC1Args);
+}
+
+void MSVCToolChain::printVerboseInfo(raw_ostream &OS) const {
+  CudaInstallation.print(OS);
+}
+
+// Windows SDKs and VC Toolchains group their contents into subdirectories based
+// on the target architecture. This function converts an llvm::Triple::ArchType
+// to the corresponding subdirectory name.
+static const char *llvmArchToWindowsSDKArch(llvm::Triple::ArchType Arch) {
+  using ArchType = llvm::Triple::ArchType;
+  switch (Arch) {
+  case ArchType::x86:
+    return "x86";
+  case ArchType::x86_64:
+    return "x64";
+  case ArchType::arm:
+    return "arm";
+  default:
+    return "";
+  }
+}
+
+// Similar to the above function, but for Visual Studios before VS2017.
+static const char *llvmArchToLegacyVCArch(llvm::Triple::ArchType Arch) {
+  using ArchType = llvm::Triple::ArchType;
+  switch (Arch) {
+  case ArchType::x86:
+    // x86 is default in legacy VC toolchains.
+    // e.g. x86 libs are directly in /lib as opposed to /lib/x86.
+    return "";
+  case ArchType::x86_64:
+    return "amd64";
+  case ArchType::arm:
+    return "arm";
+  default:
+    return "";
+  }
+}
+
+// Get the path to a specific subdirectory in the current toolchain for
+// a given target architecture.
+// VS2017 changed the VC toolchain layout, so this should be used instead
+// of hardcoding paths.
+std::string
+MSVCToolChain::getSubDirectoryPath(SubDirectoryType Type,
+                                   llvm::Triple::ArchType TargetArch) const {
+  llvm::SmallString<256> Path(VCToolChainPath);
+  switch (Type) {
+  case SubDirectoryType::Bin:
+    if (IsVS2017OrNewer) {
+      bool HostIsX64 =
+          llvm::Triple(llvm::sys::getProcessTriple()).isArch64Bit();
+      llvm::sys::path::append(Path, "bin", (HostIsX64 ? "HostX64" : "HostX86"),
+                              llvmArchToWindowsSDKArch(TargetArch));
+
+    } else {
+      llvm::sys::path::append(Path, "bin", llvmArchToLegacyVCArch(TargetArch));
+    }
+    break;
+  case SubDirectoryType::Include:
+    llvm::sys::path::append(Path, "include");
+    break;
+  case SubDirectoryType::Lib:
+    llvm::sys::path::append(
+        Path, "lib", IsVS2017OrNewer ? llvmArchToWindowsSDKArch(TargetArch)
+                                     : llvmArchToLegacyVCArch(TargetArch));
+    break;
+  }
+  return Path.str();
+}
+
+#ifdef USE_WIN32
+static bool readFullStringValue(HKEY hkey, const char *valueName,
+                                std::string &value) {
+  std::wstring WideValueName;
+  if (!llvm::ConvertUTF8toWide(valueName, WideValueName))
+    return false;
+
+  DWORD result = 0;
+  DWORD valueSize = 0;
+  DWORD type = 0;
+  // First just query for the required size.
+  result = RegQueryValueExW(hkey, WideValueName.c_str(), NULL, &type, NULL,
+                            &valueSize);
+  if (result != ERROR_SUCCESS || type != REG_SZ || !valueSize)
+    return false;
+  std::vector<BYTE> buffer(valueSize);
+  result = RegQueryValueExW(hkey, WideValueName.c_str(), NULL, NULL, &buffer[0],
+                            &valueSize);
+  if (result == ERROR_SUCCESS) {
+    std::wstring WideValue(reinterpret_cast<const wchar_t *>(buffer.data()),
+                           valueSize / sizeof(wchar_t));
+    if (valueSize && WideValue.back() == L'\0') {
+      WideValue.pop_back();
+    }
+    // The destination buffer must be empty as an invariant of the conversion
+    // function; but this function is sometimes called in a loop that passes in
+    // the same buffer, however. Simply clear it out so we can overwrite it.
+    value.clear();
+    return llvm::convertWideToUTF8(WideValue, value);
+  }
+  return false;
+}
+#endif
+
+/// \brief Read registry string.
+/// This also supports a means to look for high-versioned keys by use
+/// of a $VERSION placeholder in the key path.
+/// $VERSION in the key path is a placeholder for the version number,
+/// causing the highest value path to be searched for and used.
+/// I.e. "SOFTWARE\\Microsoft\\VisualStudio\\$VERSION".
+/// There can be additional characters in the component.  Only the numeric
+/// characters are compared.  This function only searches HKLM.
+static bool getSystemRegistryString(const char *keyPath, const char *valueName,
+                                    std::string &value, std::string *phValue) {
+#ifndef USE_WIN32
+  return false;
+#else
+  HKEY hRootKey = HKEY_LOCAL_MACHINE;
+  HKEY hKey = NULL;
+  long lResult;
+  bool returnValue = false;
+
+  const char *placeHolder = strstr(keyPath, "$VERSION");
+  std::string bestName;
+  // If we have a $VERSION placeholder, do the highest-version search.
+  if (placeHolder) {
+    const char *keyEnd = placeHolder - 1;
+    const char *nextKey = placeHolder;
+    // Find end of previous key.
+    while ((keyEnd > keyPath) && (*keyEnd != '\\'))
+      keyEnd--;
+    // Find end of key containing $VERSION.
+    while (*nextKey && (*nextKey != '\\'))
+      nextKey++;
+    size_t partialKeyLength = keyEnd - keyPath;
+    char partialKey[256];
+    if (partialKeyLength >= sizeof(partialKey))
+      partialKeyLength = sizeof(partialKey) - 1;
+    strncpy(partialKey, keyPath, partialKeyLength);
+    partialKey[partialKeyLength] = '\0';
+    HKEY hTopKey = NULL;
+    lResult = RegOpenKeyExA(hRootKey, partialKey, 0, KEY_READ | KEY_WOW64_32KEY,
+                            &hTopKey);
+    if (lResult == ERROR_SUCCESS) {
+      char keyName[256];
+      double bestValue = 0.0;
+      DWORD index, size = sizeof(keyName) - 1;
+      for (index = 0; RegEnumKeyExA(hTopKey, index, keyName, &size, NULL, NULL,
+                                    NULL, NULL) == ERROR_SUCCESS;
+           index++) {
+        const char *sp = keyName;
+        while (*sp && !isDigit(*sp))
+          sp++;
+        if (!*sp)
+          continue;
+        const char *ep = sp + 1;
+        while (*ep && (isDigit(*ep) || (*ep == '.')))
+          ep++;
+        char numBuf[32];
+        strncpy(numBuf, sp, sizeof(numBuf) - 1);
+        numBuf[sizeof(numBuf) - 1] = '\0';
+        double dvalue = strtod(numBuf, NULL);
+        if (dvalue > bestValue) {
+          // Test that InstallDir is indeed there before keeping this index.
+          // Open the chosen key path remainder.
+          bestName = keyName;
+          // Append rest of key.
+          bestName.append(nextKey);
+          lResult = RegOpenKeyExA(hTopKey, bestName.c_str(), 0,
+                                  KEY_READ | KEY_WOW64_32KEY, &hKey);
+          if (lResult == ERROR_SUCCESS) {
+            if (readFullStringValue(hKey, valueName, value)) {
+              bestValue = dvalue;
+              if (phValue)
+                *phValue = bestName;
+              returnValue = true;
+            }
+            RegCloseKey(hKey);
+          }
+        }
+        size = sizeof(keyName) - 1;
+      }
+      RegCloseKey(hTopKey);
+    }
+  } else {
+    lResult =
+        RegOpenKeyExA(hRootKey, keyPath, 0, KEY_READ | KEY_WOW64_32KEY, &hKey);
+    if (lResult == ERROR_SUCCESS) {
+      if (readFullStringValue(hKey, valueName, value))
+        returnValue = true;
+      if (phValue)
+        phValue->clear();
+      RegCloseKey(hKey);
+    }
+  }
+  return returnValue;
+#endif // USE_WIN32
+}
+
+// Find the most recent version of Universal CRT or Windows 10 SDK.
+// vcvarsqueryregistry.bat from Visual Studio 2015 sorts entries in the include
+// directory by name and uses the last one of the list.
+// So we compare entry names lexicographically to find the greatest one.
+static bool getWindows10SDKVersionFromPath(const std::string &SDKPath,
+                                           std::string &SDKVersion) {
+  SDKVersion.clear();
+
+  std::error_code EC;
+  llvm::SmallString<128> IncludePath(SDKPath);
+  llvm::sys::path::append(IncludePath, "Include");
+  for (llvm::sys::fs::directory_iterator DirIt(IncludePath, EC), DirEnd;
+       DirIt != DirEnd && !EC; DirIt.increment(EC)) {
+    if (!llvm::sys::fs::is_directory(DirIt->path()))
+      continue;
+    StringRef CandidateName = llvm::sys::path::filename(DirIt->path());
+    // If WDK is installed, there could be subfolders like "wdf" in the
+    // "Include" directory.
+    // Allow only directories which names start with "10.".
+    if (!CandidateName.startswith("10."))
+      continue;
+    if (CandidateName > SDKVersion)
+      SDKVersion = CandidateName;
+  }
+
+  return !SDKVersion.empty();
+}
+
+/// \brief Get Windows SDK installation directory.
+static bool getWindowsSDKDir(std::string &Path, int &Major,
+                             std::string &WindowsSDKIncludeVersion,
+                             std::string &WindowsSDKLibVersion) {
+  std::string RegistrySDKVersion;
+  // Try the Windows registry.
+  if (!getSystemRegistryString(
+          "SOFTWARE\\Microsoft\\Microsoft SDKs\\Windows\\$VERSION",
+          "InstallationFolder", Path, &RegistrySDKVersion))
+    return false;
+  if (Path.empty() || RegistrySDKVersion.empty())
+    return false;
+
+  WindowsSDKIncludeVersion.clear();
+  WindowsSDKLibVersion.clear();
+  Major = 0;
+  std::sscanf(RegistrySDKVersion.c_str(), "v%d.", &Major);
+  if (Major <= 7)
+    return true;
+  if (Major == 8) {
+    // Windows SDK 8.x installs libraries in a folder whose names depend on the
+    // version of the OS you're targeting.  By default choose the newest, which
+    // usually corresponds to the version of the OS you've installed the SDK on.
+    const char *Tests[] = {"winv6.3", "win8", "win7"};
+    for (const char *Test : Tests) {
+      llvm::SmallString<128> TestPath(Path);
+      llvm::sys::path::append(TestPath, "Lib", Test);
+      if (llvm::sys::fs::exists(TestPath.c_str())) {
+        WindowsSDKLibVersion = Test;
+        break;
+      }
+    }
+    return !WindowsSDKLibVersion.empty();
+  }
+  if (Major == 10) {
+    if (!getWindows10SDKVersionFromPath(Path, WindowsSDKIncludeVersion))
+      return false;
+    WindowsSDKLibVersion = WindowsSDKIncludeVersion;
+    return true;
+  }
+  // Unsupported SDK version
+  return false;
+}
+
+// Gets the library path required to link against the Windows SDK.
+bool MSVCToolChain::getWindowsSDKLibraryPath(std::string &path) const {
+  std::string sdkPath;
+  int sdkMajor = 0;
+  std::string windowsSDKIncludeVersion;
+  std::string windowsSDKLibVersion;
+
+  path.clear();
+  if (!getWindowsSDKDir(sdkPath, sdkMajor, windowsSDKIncludeVersion,
+                        windowsSDKLibVersion))
+    return false;
+
+  llvm::SmallString<128> libPath(sdkPath);
+  llvm::sys::path::append(libPath, "Lib");
+  if (sdkMajor >= 8) {
+    llvm::sys::path::append(libPath, windowsSDKLibVersion, "um",
+                            llvmArchToWindowsSDKArch(getArch()));
+  } else {
+    switch (getArch()) {
+    // In Windows SDK 7.x, x86 libraries are directly in the Lib folder.
+    case llvm::Triple::x86:
+      break;
+    case llvm::Triple::x86_64:
+      llvm::sys::path::append(libPath, "x64");
+      break;
+    case llvm::Triple::arm:
+      // It is not necessary to link against Windows SDK 7.x when targeting ARM.
+      return false;
+    default:
+      return false;
+    }
+  }
+
+  path = libPath.str();
+  return true;
+}
+
+// Check if the Include path of a specified version of Visual Studio contains
+// specific header files. If not, they are probably shipped with Universal CRT.
+bool MSVCToolChain::useUniversalCRT() const {
+  llvm::SmallString<128> TestPath(
+      getSubDirectoryPath(SubDirectoryType::Include));
+  llvm::sys::path::append(TestPath, "stdlib.h");
+  return !llvm::sys::fs::exists(TestPath);
+}
+
+static bool getUniversalCRTSdkDir(std::string &Path, std::string &UCRTVersion) {
+  // vcvarsqueryregistry.bat for Visual Studio 2015 queries the registry
+  // for the specific key "KitsRoot10". So do we.
+  if (!getSystemRegistryString(
+          "SOFTWARE\\Microsoft\\Windows Kits\\Installed Roots", "KitsRoot10",
+          Path, nullptr))
+    return false;
+
+  return getWindows10SDKVersionFromPath(Path, UCRTVersion);
+}
+
+bool MSVCToolChain::getUniversalCRTLibraryPath(std::string &Path) const {
+  std::string UniversalCRTSdkPath;
+  std::string UCRTVersion;
+
+  Path.clear();
+  if (!getUniversalCRTSdkDir(UniversalCRTSdkPath, UCRTVersion))
+    return false;
+
+  StringRef ArchName = llvmArchToWindowsSDKArch(getArch());
+  if (ArchName.empty())
+    return false;
+
+  llvm::SmallString<128> LibPath(UniversalCRTSdkPath);
+  llvm::sys::path::append(LibPath, "Lib", UCRTVersion, "ucrt", ArchName);
+
+  Path = LibPath.str();
+  return true;
+}
+
+static VersionTuple getMSVCVersionFromTriple(const llvm::Triple &Triple) {
+  unsigned Major, Minor, Micro;
+  Triple.getEnvironmentVersion(Major, Minor, Micro);
+  if (Major || Minor || Micro)
+    return VersionTuple(Major, Minor, Micro);
+  return VersionTuple();
+}
+
+static VersionTuple getMSVCVersionFromExe(const std::string &BinDir) {
+  VersionTuple Version;
+#ifdef USE_WIN32
+  SmallString<128> ClExe(BinDir);
+  llvm::sys::path::append(ClExe, "cl.exe");
+
+  std::wstring ClExeWide;
+  if (!llvm::ConvertUTF8toWide(ClExe.c_str(), ClExeWide))
+    return Version;
+
+  const DWORD VersionSize = ::GetFileVersionInfoSizeW(ClExeWide.c_str(),
+                                                      nullptr);
+  if (VersionSize == 0)
+    return Version;
+
+  SmallVector<uint8_t, 4 * 1024> VersionBlock(VersionSize);
+  if (!::GetFileVersionInfoW(ClExeWide.c_str(), 0, VersionSize,
+                             VersionBlock.data()))
+    return Version;
+
+  VS_FIXEDFILEINFO *FileInfo = nullptr;
+  UINT FileInfoSize = 0;
+  if (!::VerQueryValueW(VersionBlock.data(), L"\\",
+                        reinterpret_cast<LPVOID *>(&FileInfo), &FileInfoSize) ||
+      FileInfoSize < sizeof(*FileInfo))
+    return Version;
+
+  const unsigned Major = (FileInfo->dwFileVersionMS >> 16) & 0xFFFF;
+  const unsigned Minor = (FileInfo->dwFileVersionMS      ) & 0xFFFF;
+  const unsigned Micro = (FileInfo->dwFileVersionLS >> 16) & 0xFFFF;
+
+  Version = VersionTuple(Major, Minor, Micro);
+#endif
+  return Version;
+}
+
+void MSVCToolChain::AddSystemIncludeWithSubfolder(
+    const ArgList &DriverArgs, ArgStringList &CC1Args,
+    const std::string &folder, const Twine &subfolder1, const Twine &subfolder2,
+    const Twine &subfolder3) const {
+  llvm::SmallString<128> path(folder);
+  llvm::sys::path::append(path, subfolder1, subfolder2, subfolder3);
+  addSystemInclude(DriverArgs, CC1Args, path);
+}
+
+void MSVCToolChain::AddClangSystemIncludeArgs(const ArgList &DriverArgs,
+                                              ArgStringList &CC1Args) const {
+  if (DriverArgs.hasArg(options::OPT_nostdinc))
+    return;
+
+  if (!DriverArgs.hasArg(options::OPT_nobuiltininc)) {
+    AddSystemIncludeWithSubfolder(DriverArgs, CC1Args, getDriver().ResourceDir,
+                                  "include");
+  }
+
+  // Add %INCLUDE%-like directories from the -imsvc flag.
+  for (const auto &Path : DriverArgs.getAllArgValues(options::OPT__SLASH_imsvc))
+    addSystemInclude(DriverArgs, CC1Args, Path);
+
+  if (DriverArgs.hasArg(options::OPT_nostdlibinc))
+    return;
+
+  // Honor %INCLUDE%. It should know essential search paths with vcvarsall.bat.
+  if (llvm::Optional<std::string> cl_include_dir =
+          llvm::sys::Process::GetEnv("INCLUDE")) {
+    SmallVector<StringRef, 8> Dirs;
+    StringRef(*cl_include_dir)
+        .split(Dirs, ";", /*MaxSplit=*/-1, /*KeepEmpty=*/false);
+    for (StringRef Dir : Dirs)
+      addSystemInclude(DriverArgs, CC1Args, Dir);
+    if (!Dirs.empty())
+      return;
+  }
+
+  // When built with access to the proper Windows APIs, try to actually find
+  // the correct include paths first.
+  if (!VCToolChainPath.empty()) {
+    addSystemInclude(DriverArgs, CC1Args,
+                     getSubDirectoryPath(SubDirectoryType::Include));
+
+    if (useUniversalCRT()) {
+      std::string UniversalCRTSdkPath;
+      std::string UCRTVersion;
+      if (getUniversalCRTSdkDir(UniversalCRTSdkPath, UCRTVersion)) {
+        AddSystemIncludeWithSubfolder(DriverArgs, CC1Args, UniversalCRTSdkPath,
+                                      "Include", UCRTVersion, "ucrt");
+      }
+    }
+
+    std::string WindowsSDKDir;
+    int major;
+    std::string windowsSDKIncludeVersion;
+    std::string windowsSDKLibVersion;
+    if (getWindowsSDKDir(WindowsSDKDir, major, windowsSDKIncludeVersion,
+                         windowsSDKLibVersion)) {
+      if (major >= 8) {
+        // Note: windowsSDKIncludeVersion is empty for SDKs prior to v10.
+        // Anyway, llvm::sys::path::append is able to manage it.
+        AddSystemIncludeWithSubfolder(DriverArgs, CC1Args, WindowsSDKDir,
+                                      "include", windowsSDKIncludeVersion,
+                                      "shared");
+        AddSystemIncludeWithSubfolder(DriverArgs, CC1Args, WindowsSDKDir,
+                                      "include", windowsSDKIncludeVersion,
+                                      "um");
+        AddSystemIncludeWithSubfolder(DriverArgs, CC1Args, WindowsSDKDir,
+                                      "include", windowsSDKIncludeVersion,
+                                      "winrt");
+      } else {
+        AddSystemIncludeWithSubfolder(DriverArgs, CC1Args, WindowsSDKDir,
+                                      "include");
+      }
+    }
+
+    return;
+  }
+
+#if defined(LLVM_ON_WIN32)
+  // As a fallback, select default install paths.
+  // FIXME: Don't guess drives and paths like this on Windows.
+  const StringRef Paths[] = {
+    "C:/Program Files/Microsoft Visual Studio 10.0/VC/include",
+    "C:/Program Files/Microsoft Visual Studio 9.0/VC/include",
+    "C:/Program Files/Microsoft Visual Studio 9.0/VC/PlatformSDK/Include",
+    "C:/Program Files/Microsoft Visual Studio 8/VC/include",
+    "C:/Program Files/Microsoft Visual Studio 8/VC/PlatformSDK/Include"
+  };
+  addSystemIncludes(DriverArgs, CC1Args, Paths);
+#endif
+}
+
+void MSVCToolChain::AddClangCXXStdlibIncludeArgs(const ArgList &DriverArgs,
+                                                 ArgStringList &CC1Args) const {
+  // FIXME: There should probably be logic here to find libc++ on Windows.
+}
+
+VersionTuple MSVCToolChain::computeMSVCVersion(const Driver *D,
+                                               const ArgList &Args) const {
+  bool IsWindowsMSVC = getTriple().isWindowsMSVCEnvironment();
+  VersionTuple MSVT = ToolChain::computeMSVCVersion(D, Args);
+  if (MSVT.empty())
+    MSVT = getMSVCVersionFromTriple(getTriple());
+  if (MSVT.empty() && IsWindowsMSVC)
+    MSVT = getMSVCVersionFromExe(getSubDirectoryPath(SubDirectoryType::Bin));
+  if (MSVT.empty() &&
+      Args.hasFlag(options::OPT_fms_extensions, options::OPT_fno_ms_extensions,
+                   IsWindowsMSVC)) {
+    // -fms-compatibility-version=18.00 is default.
+    // FIXME: Consider bumping this to 19 (MSVC2015) soon.
+    MSVT = VersionTuple(18);
+  }
+  return MSVT;
+}
+
+std::string
+MSVCToolChain::ComputeEffectiveClangTriple(const ArgList &Args,
+                                           types::ID InputType) const {
+  // The MSVC version doesn't care about the architecture, even though it
+  // may look at the triple internally.
+  VersionTuple MSVT = computeMSVCVersion(/*D=*/nullptr, Args);
+  MSVT = VersionTuple(MSVT.getMajor(), MSVT.getMinor().getValueOr(0),
+                      MSVT.getSubminor().getValueOr(0));
+
+  // For the rest of the triple, however, a computed architecture name may
+  // be needed.
+  llvm::Triple Triple(ToolChain::ComputeEffectiveClangTriple(Args, InputType));
+  if (Triple.getEnvironment() == llvm::Triple::MSVC) {
+    StringRef ObjFmt = Triple.getEnvironmentName().split('-').second;
+    if (ObjFmt.empty())
+      Triple.setEnvironmentName((Twine("msvc") + MSVT.getAsString()).str());
+    else
+      Triple.setEnvironmentName(
+          (Twine("msvc") + MSVT.getAsString() + Twine('-') + ObjFmt).str());
+  }
+  return Triple.getTriple();
+}
+
+SanitizerMask MSVCToolChain::getSupportedSanitizers() const {
+  SanitizerMask Res = ToolChain::getSupportedSanitizers();
+  Res |= SanitizerKind::Address;
+  return Res;
+}
+
+static void TranslateOptArg(Arg *A, llvm::opt::DerivedArgList &DAL,
+                            bool SupportsForcingFramePointer,
+                            const char *ExpandChar, const OptTable &Opts) {
+  assert(A->getOption().matches(options::OPT__SLASH_O));
+
+  StringRef OptStr = A->getValue();
+  for (size_t I = 0, E = OptStr.size(); I != E; ++I) {
+    const char &OptChar = *(OptStr.data() + I);
+    switch (OptChar) {
+    default:
+      break;
+    case '1':
+    case '2':
+    case 'x':
+    case 'd':
+      if (&OptChar == ExpandChar) {
+        if (OptChar == 'd') {
+          DAL.AddFlagArg(A, Opts.getOption(options::OPT_O0));
+        } else {
+          if (OptChar == '1') {
+            DAL.AddJoinedArg(A, Opts.getOption(options::OPT_O), "s");
+          } else if (OptChar == '2' || OptChar == 'x') {
+            DAL.AddFlagArg(A, Opts.getOption(options::OPT_fbuiltin));
+            DAL.AddJoinedArg(A, Opts.getOption(options::OPT_O), "2");
+          }
+          if (SupportsForcingFramePointer &&
+              !DAL.hasArgNoClaim(options::OPT_fno_omit_frame_pointer))
+            DAL.AddFlagArg(A,
+                           Opts.getOption(options::OPT_fomit_frame_pointer));
+          if (OptChar == '1' || OptChar == '2')
+            DAL.AddFlagArg(A,
+                           Opts.getOption(options::OPT_ffunction_sections));
+        }
+      }
+      break;
+    case 'b':
+      if (I + 1 != E && isdigit(OptStr[I + 1])) {
+        switch (OptStr[I + 1]) {
+        case '0':
+          DAL.AddFlagArg(A, Opts.getOption(options::OPT_fno_inline));
+          break;
+        case '1':
+          DAL.AddFlagArg(A, Opts.getOption(options::OPT_finline_hint_functions));
+          break;
+        case '2':
+          DAL.AddFlagArg(A, Opts.getOption(options::OPT_finline_functions));
+          break;
+        }
+        ++I;
+      }
+      break;
+    case 'g':
+      break;
+    case 'i':
+      if (I + 1 != E && OptStr[I + 1] == '-') {
+        ++I;
+        DAL.AddFlagArg(A, Opts.getOption(options::OPT_fno_builtin));
+      } else {
+        DAL.AddFlagArg(A, Opts.getOption(options::OPT_fbuiltin));
+      }
+      break;
+    case 's':
+      DAL.AddJoinedArg(A, Opts.getOption(options::OPT_O), "s");
+      break;
+    case 't':
+      DAL.AddJoinedArg(A, Opts.getOption(options::OPT_O), "2");
+      break;
+    case 'y': {
+      bool OmitFramePointer = true;
+      if (I + 1 != E && OptStr[I + 1] == '-') {
+        OmitFramePointer = false;
+        ++I;
+      }
+      if (SupportsForcingFramePointer) {
+        if (OmitFramePointer)
+          DAL.AddFlagArg(A,
+                         Opts.getOption(options::OPT_fomit_frame_pointer));
+        else
+          DAL.AddFlagArg(
+              A, Opts.getOption(options::OPT_fno_omit_frame_pointer));
+      } else {
+        // Don't warn about /Oy- in 64-bit builds (where
+        // SupportsForcingFramePointer is false).  The flag having no effect
+        // there is a compiler-internal optimization, and people shouldn't have
+        // to special-case their build files for 64-bit clang-cl.
+        A->claim();
+      }
+      break;
+    }
+    }
+  }
+}
+
+static void TranslateDArg(Arg *A, llvm::opt::DerivedArgList &DAL,
+                          const OptTable &Opts) {
+  assert(A->getOption().matches(options::OPT_D));
+
+  StringRef Val = A->getValue();
+  size_t Hash = Val.find('#');
+  if (Hash == StringRef::npos || Hash > Val.find('=')) {
+    DAL.append(A);
+    return;
+  }
+
+  std::string NewVal = Val;
+  NewVal[Hash] = '=';
+  DAL.AddJoinedArg(A, Opts.getOption(options::OPT_D), NewVal);
+}
+
+llvm::opt::DerivedArgList *
+MSVCToolChain::TranslateArgs(const llvm::opt::DerivedArgList &Args,
+                             StringRef BoundArch, Action::OffloadKind) const {
+  DerivedArgList *DAL = new DerivedArgList(Args.getBaseArgs());
+  const OptTable &Opts = getDriver().getOpts();
+
+  // /Oy and /Oy- only has an effect under X86-32.
+  bool SupportsForcingFramePointer = getArch() == llvm::Triple::x86;
+
+  // The -O[12xd] flag actually expands to several flags.  We must desugar the
+  // flags so that options embedded can be negated.  For example, the '-O2' flag
+  // enables '-Oy'.  Expanding '-O2' into its constituent flags allows us to
+  // correctly handle '-O2 -Oy-' where the trailing '-Oy-' disables a single
+  // aspect of '-O2'.
+  //
+  // Note that this expansion logic only applies to the *last* of '[12xd]'.
+
+  // First step is to search for the character we'd like to expand.
+  const char *ExpandChar = nullptr;
+  for (Arg *A : Args) {
+    if (!A->getOption().matches(options::OPT__SLASH_O))
+      continue;
+    StringRef OptStr = A->getValue();
+    for (size_t I = 0, E = OptStr.size(); I != E; ++I) {
+      char OptChar = OptStr[I];
+      char PrevChar = I > 0 ? OptStr[I - 1] : '0';
+      if (PrevChar == 'b') {
+        // OptChar does not expand; it's an argument to the previous char.
+        continue;
+      }
+      if (OptChar == '1' || OptChar == '2' || OptChar == 'x' || OptChar == 'd')
+        ExpandChar = OptStr.data() + I;
+    }
+  }
+
+  for (Arg *A : Args) {
+    if (A->getOption().matches(options::OPT__SLASH_O)) {
+      // The -O flag actually takes an amalgam of other options.  For example,
+      // '/Ogyb2' is equivalent to '/Og' '/Oy' '/Ob2'.
+      TranslateOptArg(A, *DAL, SupportsForcingFramePointer, ExpandChar, Opts);
+    } else if (A->getOption().matches(options::OPT_D)) {
+      // Translate -Dfoo#bar into -Dfoo=bar.
+      TranslateDArg(A, *DAL, Opts);
+    } else {
+      DAL->append(A);
+    }
+  }
+
+  return DAL;
+}