Resubmit "Improve Windows toolchain support for non-standard environments."

[zturner]

Summary

This resubmits change r220226.  That change broke the chromium
build bots because chromium it ships an hermetic MSVC toolchain
that it expects clang to fallback to by finding it on the path.

This patch fixes the issue by bumping up the prioritization of PATH
when looking for MSVC binaries.

[rnk]

lib/Driver/WindowsToolChain.cpp

220 ↗

(On Diff #15203)

I don't think we need to sink this logic into the toolchain, we can probably keep it local to the fallback code, just changing the order of the check for the VS install dir to come after we've done the PATH search.

226 ↗

(On Diff #15203)

This doesn't seem right, we need the path to VS/VC/bin or VS/VC/bin/amd64. I don't think we need to have this first case.

[hans]

It seems the patch is based on top off the patch which got reverted. It would be better if it was relative to the current trunk.

I tried this on the Chromium build and it worked.

[hans]

lib/Driver/WindowsToolChain.cpp

218 ↗

(On Diff #15203)

I wonder if we should check PATH first.

If the user runs "cl.exe", she expects the one on PATH to be run. If she uses clang-cl.exe instead, and we fall back, that's the cl.exe we should use.

[zturner]

Fix review issues. Also check the target triple to determine which toolchain to use (x86, x64, or arm).

[zturner]

In D5892#5, @hans wrote:

It seems the patch is based on top off the patch which got reverted. It would be better if it was relative to the current trunk.

I tried this on the Chromium build and it worked.

That's strange, it should be based off of current trunk.

lib/Driver/WindowsToolChain.cpp

226 ↗

(On Diff #15203)

I kind of like checking VCINSTALLDIR first, because the only way that's set is if someone runs vcvars, which *also* sets PATH. The only way checking VCINSTALLDIR first causes a problem is if someone runs vcvars, then further modifies the PATH to stick something else first. If someone does that I feel like we could say "sorry, your'e on your own now". PATH is kind of the garbage disposal of the environment, and everyone just dumps what they need into PATH. So it's more likely to get polluted than VCINSTALLDIR, which is much more specific.

[zturner]

Patch should be based off of current ToT now, I originally ran git revert <the original revert>, and then submitted this on top of that. I squashed the two now, so this should be based on top of ToT.

[zturner]

Rebase against ToT again, someone renamed this class @.@

[hans]

lib/Driver/MSVCToolChain.cpp

218

The Windows toolchain was renamed to MSVCToolChain in r220362.

225

Should this use llvm::sys::Process::GetEnv like below?

228

Should this append VC\bin ?

When I applied this patch, clang no longer finds link.exe in my VS2012 environment.

VCINSTALLDIR is set to C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\ and link.exe is at C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\bin\link.exe

If I unset VSINSTALLDIR it seems to work due to the PATH walking below.

[zturner]

Hopefully this fixes all the issues. Now, if VCINSTALLDIR is set, it only appends "bin" (since the VC part is already on the path).

[hans]

Seems to work for me :)

[zturner]

Closed by commit rL220424 (authored by @zturner).

lib/Driver/MSVCToolChain.cpp

 //===--- 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 "ToolChains.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 "llvm/ADT/StringExtras.h"
 #include "llvm/Config/llvm-config.h"
 #include "llvm/Option/Arg.h"
 #include "llvm/Option/ArgList.h"
 #include "llvm/Support/ErrorHandling.h"
-#include "llvm/Support/Path.h"
+#include "llvm/Support/FileSystem.h"
+#include "llvm/Support/Process.h"
 
 // Include the necessary headers to interface with the Windows registry and
 // environment.
 #if defined(LLVM_ON_WIN32)
 #define USE_WIN32
 #endif
 
 #ifdef USE_WIN32

 bool MSVCToolChain::isPIEDefault() const {
   return false;
 }
 
 bool MSVCToolChain::isPICDefaultForced() const {
   return getArch() == llvm::Triple::x86_64;
 }
 
+#ifdef USE_WIN32
+static bool readFullStringValue(HKEY hkey, const char *valueName,
+                                std::string &value) {
+  // FIXME: We should be using the W versions of the registry functions, but
+  // doing so requires UTF8 / UTF16 conversions similar to how we handle command
+  // line arguments.  The UTF8 conversion functions are not exposed publicly
+  // from LLVM though, so in order to do this we will probably need to create
+  // a registry abstraction in LLVMSupport that is Windows only.
+  DWORD result = 0;
+  DWORD valueSize = 0;
+  DWORD type = 0;
+  // First just query for the required size.
+  result = RegQueryValueEx(hkey, valueName, NULL, &type, NULL, &valueSize);
+  if (result != ERROR_SUCCESS || type != REG_SZ)
+    return false;
+  std::vector<BYTE> buffer(valueSize);
+  result = RegQueryValueEx(hkey, valueName, NULL, NULL, &buffer[0], &valueSize);
+  if (result == ERROR_SUCCESS)
+    value.assign(reinterpret_cast<const char *>(buffer.data()));
+  return result;
+}
+#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.
 /// $VERSION in the key path is a placeholder for the version number,
 /// causing the highest value path to be searched for and used.
-/// I.e. "HKEY_LOCAL_MACHINE\\SOFTWARE\\Microsoft\\VisualStudio\\$VERSION".
-/// There can be additional characters in the component.  Only the numberic
-/// characters are compared.
+/// 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,
-                                    char *value, size_t maxLength) {
+                                    std::string &value, std::string *phValue) {
 #ifndef USE_WIN32
   return false;
 #else
-  HKEY hRootKey = NULL;
+  HKEY hRootKey = HKEY_LOCAL_MACHINE;
   HKEY hKey = NULL;
-  const char* subKey = NULL;
-  DWORD valueType;
-  DWORD valueSize = maxLength - 1;
+  DWORD valueSize = 0;
   long lResult;
   bool returnValue = false;
 
-  if (strncmp(keyPath, "HKEY_CLASSES_ROOT\\", 18) == 0) {
-    hRootKey = HKEY_CLASSES_ROOT;
-    subKey = keyPath + 18;
-  } else if (strncmp(keyPath, "HKEY_USERS\\", 11) == 0) {
-    hRootKey = HKEY_USERS;
-    subKey = keyPath + 11;
-  } else if (strncmp(keyPath, "HKEY_LOCAL_MACHINE\\", 19) == 0) {
-    hRootKey = HKEY_LOCAL_MACHINE;
-    subKey = keyPath + 19;
-  } else if (strncmp(keyPath, "HKEY_CURRENT_USER\\", 18) == 0) {
-    hRootKey = HKEY_CURRENT_USER;
-    subKey = keyPath + 18;
-  } else {
-    return false;
-  }
-
-  const char *placeHolder = strstr(subKey, "$VERSION");
-  char bestName[256];
-  bestName[0] = '\0';
+  const char *placeHolder = strstr(keyPath, "$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 > subKey) && (*keyEnd != '\\'))
+    while ((keyEnd > keyPath) && (*keyEnd != '\\'))
       keyEnd--;
     // Find end of key containing $VERSION.
     while (*nextKey && (*nextKey != '\\'))
       nextKey++;
-    size_t partialKeyLength = keyEnd - subKey;
+    size_t partialKeyLength = keyEnd - keyPath;
     char partialKey[256];
     if (partialKeyLength > sizeof(partialKey))
       partialKeyLength = sizeof(partialKey);
-    strncpy(partialKey, subKey, partialKeyLength);
+    strncpy(partialKey, keyPath, partialKeyLength);
     partialKey[partialKeyLength] = '\0';
     HKEY hTopKey = NULL;
     lResult = RegOpenKeyEx(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;
if (lResult == ERROR_SUCCESS) {
           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.
-          strcpy(bestName, keyName);
+          bestName = keyName;
           // Append rest of key.
-          strncat(bestName, nextKey, sizeof(bestName) - 1);
-          bestName[sizeof(bestName) - 1] = '\0';
-          lResult = RegOpenKeyEx(hTopKey, bestName, 0,
+          bestName.append(nextKey);
+          lResult = RegOpenKeyEx(hTopKey, bestName.c_str(), 0,
                                  KEY_READ | KEY_WOW64_32KEY, &hKey);
           if (lResult == ERROR_SUCCESS) {
-            lResult = RegQueryValueEx(hKey, valueName, NULL, &valueType,
-              (LPBYTE)value, &valueSize);
+            lResult = readFullStringValue(hKey, valueName, value);
             if (lResult == ERROR_SUCCESS) {
               bestValue = dvalue;
+              if (phValue)
+                *phValue = bestName;
               returnValue = true;
             }
             RegCloseKey(hKey);
           }
         }
         size = sizeof(keyName) - 1;
       }
       RegCloseKey(hTopKey);
     }
   } else {
-    lResult = RegOpenKeyEx(hRootKey, subKey, 0, KEY_READ | KEY_WOW64_32KEY,
-                           &hKey);
+    lResult =
+        RegOpenKeyEx(hRootKey, keyPath, 0, KEY_READ | KEY_WOW64_32KEY, &hKey);
     if (lResult == ERROR_SUCCESS) {
-      lResult = RegQueryValueEx(hKey, valueName, NULL, &valueType,
-        (LPBYTE)value, &valueSize);
+      lResult = readFullStringValue(hKey, valueName, value);
       if (lResult == ERROR_SUCCESS)
         returnValue = true;
+      if (phValue)
+        phValue->clear();
       RegCloseKey(hKey);
     }
   }
   return returnValue;
 #endif // USE_WIN32
 }
 
 /// \brief Get Windows SDK installation directory.
-static bool getWindowsSDKDir(std::string &path) {
-  char windowsSDKInstallDir[256];
+bool Windows::getWindowsSDKDir(std::string &path, int &major,
+                               int &minor) const {
+  std::string sdkVersion;
   // Try the Windows registry.
   bool hasSDKDir = getSystemRegistryString(
-   "HKEY_LOCAL_MACHINE\\SOFTWARE\\Microsoft\\Microsoft SDKs\\Windows\\$VERSION",
-                                           "InstallationFolder",
-                                           windowsSDKInstallDir,
-                                           sizeof(windowsSDKInstallDir) - 1);
-    // If we have both vc80 and vc90, pick version we were compiled with.
-  if (hasSDKDir && windowsSDKInstallDir[0]) {
-    path = windowsSDKInstallDir;
+      "SOFTWARE\\Microsoft\\Microsoft SDKs\\Windows\\$VERSION",
+      "InstallationFolder", path, &sdkVersion);
+  if (!sdkVersion.empty())
+    ::sscanf(sdkVersion.c_str(), "v%d.%d", &major, &minor);
+  return hasSDKDir && !path.empty();
+}
+
+// Get the location to use for Visual Studio binaries.  The location priority
+// is: %VCINSTALLDIR% > %PATH% > newest copy of Visual Studio installed on
+// system (as reported by the registry).
+bool Windows::getVisualStudioBinariesFolder(const char *clangProgramPath,
+                                            std::string &path) const {
+  path.clear();
+
+  SmallString<128> BinDir;
+
+  // First check the environment variables that vsvars32.bat sets.
+  const char *vcinstalldir = getenv("VCINSTALLDIR");
+  if (vcinstalldir) {
+    BinDir = vcinstalldir;
+    llvm::sys::path::append(BinDir, "VC");
+  } else {
+    // Next walk the PATH, trying to find a cl.exe in the path.  If we find one,
+    // use that.  However, make sure it's not clang's cl.exe.
+    llvm::Optional<std::string> OptPath = llvm::sys::Process::GetEnv("PATH");
+    if (OptPath.hasValue()) {
+      const char EnvPathSeparatorStr[] = {llvm::sys::EnvPathSeparator, '\0'};
+      SmallVector<StringRef, 8> PathSegments;
+      llvm::SplitString(OptPath.getValue(), PathSegments, EnvPathSeparatorStr);
+
+      for (StringRef PathSegment : PathSegments) {
+        if (PathSegment.empty())
+          continue;
+
+        SmallString<128> FilePath(PathSegment);
+        llvm::sys::path::append(FilePath, "cl.exe");
+        if (llvm::sys::fs::can_execute(FilePath.c_str()) &&
+            !llvm::sys::fs::equivalent(FilePath.c_str(), clangProgramPath)) {
+          // If we found it on the PATH, use it exactly as is with no
+          // modifications.
+          path = PathSegment;
           return true;
         }
+      }
+    }
+
+    std::string installDir;
+    // With no VCINSTALLDIR and nothing on the PATH, if we can't find it in the
+    // registry then we have no choice but to fail.
+    if (!getVisualStudioInstallDir(installDir))
+      return false;
+
+    // Regardless of what binary we're ultimately trying to find, we make sure
+    // that this is a Visual Studio directory by checking for cl.exe.  We use
+    // cl.exe instead of other binaries like link.exe because programs such as
+    // GnuWin32 also have a utility called link.exe, so cl.exe is the least
+    // ambiguous.
+    BinDir = installDir;
+    llvm::sys::path::append(BinDir, "VC\\bin");
+    SmallString<128> ClPath(BinDir);
+    llvm::sys::path::append(ClPath, "cl.exe");
+
+    if (!llvm::sys::fs::can_execute(ClPath.c_str()))
       return false;
   }
 
+  if (BinDir.empty())
+    return false;
+
+  switch (getArch()) {
+  case llvm::Triple::x86:
+    break;
+  case llvm::Triple::x86_64:
+    llvm::sys::path::append(BinDir, "amd64");
+    break;
+  case llvm::Triple::arm:
+    llvm::sys::path::append(BinDir, "arm");
+    break;
+  default:
+    // Whatever this is, Visual Studio doesn't have a toolchain for it.
+    return false;
+  }
+  path = BinDir.str();
+  return true;
+}
+
 // Get Visual Studio installation directory.
-static bool getVisualStudioDir(std::string &path) {
+bool Windows::getVisualStudioInstallDir(std::string &path) const {
   // First check the environment variables that vsvars32.bat sets.
-  const char* vcinstalldir = getenv("VCINSTALLDIR");
+  const char *vcinstalldir = getenv("VCINSTALLDIR");
   if (vcinstalldir) {
-    char *p = const_cast<char *>(strstr(vcinstalldir, "\\VC"));
-    if (p)
-      *p = '\0';
     path = vcinstalldir;
+    path = path.substr(0, path.find("\\VC"));
     return true;
   }
 
-  char vsIDEInstallDir[256];
-  char vsExpressIDEInstallDir[256];
+  std::string vsIDEInstallDir;
+  std::string vsExpressIDEInstallDir;
   // Then try the windows registry.
-  bool hasVCDir = getSystemRegistryString(
-    "HKEY_LOCAL_MACHINE\\SOFTWARE\\Microsoft\\VisualStudio\\$VERSION",
-    "InstallDir", vsIDEInstallDir, sizeof(vsIDEInstallDir) - 1);
-  bool hasVCExpressDir = getSystemRegistryString(
-    "HKEY_LOCAL_MACHINE\\SOFTWARE\\Microsoft\\VCExpress\\$VERSION",
-    "InstallDir", vsExpressIDEInstallDir, sizeof(vsExpressIDEInstallDir) - 1);
-    // If we have both vc80 and vc90, pick version we were compiled with.
-  if (hasVCDir && vsIDEInstallDir[0]) {
-    char *p = (char*)strstr(vsIDEInstallDir, "\\Common7\\IDE");
-    if (p)
-      *p = '\0';
-    path = vsIDEInstallDir;
+  bool hasVCDir =
+      getSystemRegistryString("SOFTWARE\\Microsoft\\VisualStudio\\$VERSION",
+                              "InstallDir", vsIDEInstallDir, nullptr);
+  if (hasVCDir && !vsIDEInstallDir.empty()) {
+    path = vsIDEInstallDir.substr(0, vsIDEInstallDir.find("\\Common7\\IDE"));
     return true;
   }
 
-  if (hasVCExpressDir && vsExpressIDEInstallDir[0]) {
-    char *p = (char*)strstr(vsExpressIDEInstallDir, "\\Common7\\IDE");
-    if (p)
-      *p = '\0';
-    path = vsExpressIDEInstallDir;
+  bool hasVCExpressDir =
+      getSystemRegistryString("SOFTWARE\\Microsoft\\VCExpress\\$VERSION",
+                              "InstallDir", vsExpressIDEInstallDir, nullptr);
+  if (hasVCExpressDir && !vsExpressIDEInstallDir.empty()) {
+    path = vsExpressIDEInstallDir.substr(
+        0, vsIDEInstallDir.find("\\Common7\\IDE"));
     return true;
   }
 
   // Try the environment.
+  const char *vs120comntools = getenv("VS120COMNTOOLS");
   const char *vs100comntools = getenv("VS100COMNTOOLS");
   const char *vs90comntools = getenv("VS90COMNTOOLS");
   const char *vs80comntools = getenv("VS80COMNTOOLS");
 
   const char *vscomntools = nullptr;
 
   // Find any version we can
-  if (vs100comntools)
+  if (vs120comntools)
+    vscomntools = vs120comntools;
+  else if (vs100comntools)
     vscomntools = vs100comntools;
   else if (vs90comntools)
     vscomntools = vs90comntools;
   else if (vs80comntools)
     vscomntools = vs80comntools;
 
   if (vscomntools && *vscomntools) {
     const char *p = strstr(vscomntools, "\\Common7\\Tools");
     path = p ? std::string(vscomntools, p) : vscomntools;
     return true;
   }
   return false;
 }
 
+void MSVCToolChain::AddSystemIncludeWithSubfolder(const ArgList &DriverArgs,
+                                                   ArgStringList &CC1Args,
+                                                   const std::string &folder,
+                                                   const char *subfolder) const {
+  llvm::SmallString<128> path(folder);
+  llvm::sys::path::append(path, subfolder);
+  addSystemInclude(DriverArgs, CC1Args, path.str());
+}
+
 void MSVCToolChain::AddClangSystemIncludeArgs(const ArgList &DriverArgs,
                                               ArgStringList &CC1Args) const {
   if (DriverArgs.hasArg(options::OPT_nostdinc))
     return;
 
   if (!DriverArgs.hasArg(options::OPT_nobuiltininc)) {
     SmallString<128> P(getDriver().ResourceDir);
     llvm::sys::path::append(P, "include");
StringRef(cl_include_dir)
         .split(Dirs, ";", /*MaxSplit=*/-1, /*KeepEmpty=*/false);
     for (StringRef Dir : Dirs)
       addSystemInclude(DriverArgs, CC1Args, Dir);
     if (!Dirs.empty())
       return;
   }
 
   std::string VSDir;
-  std::string WindowsSDKDir;
 
   // When built with access to the proper Windows APIs, try to actually find
   // the correct include paths first.
-  if (getVisualStudioDir(VSDir)) {
-    SmallString<128> P;
-    P = VSDir;
-    llvm::sys::path::append(P, "VC\\include");
-    addSystemInclude(DriverArgs, CC1Args, P.str());
-    if (getWindowsSDKDir(WindowsSDKDir)) {
-      P = WindowsSDKDir;
-      llvm::sys::path::append(P, "include");
-      addSystemInclude(DriverArgs, CC1Args, P.str());
+  if (getVisualStudioInstallDir(VSDir)) {
+    AddSystemIncludeWithSubfolder(DriverArgs, CC1Args, VSDir, "VC\\include");
+
+    std::string WindowsSDKDir;
+    int major, minor;
+    if (getWindowsSDKDir(WindowsSDKDir, major, minor)) {
+      if (major >= 8) {
+        AddSystemIncludeWithSubfolder(DriverArgs, CC1Args, WindowsSDKDir,
+                                      "include\\shared");
+        AddSystemIncludeWithSubfolder(DriverArgs, CC1Args, WindowsSDKDir,
+                                      "include\\um");
+        AddSystemIncludeWithSubfolder(DriverArgs, CC1Args, WindowsSDKDir,
+                                      "include\\winrt");
       } else {
-      P = VSDir;
-      llvm::sys::path::append(P, "VC\\PlatformSDK\\Include");
-      addSystemInclude(DriverArgs, CC1Args, P.str());
+        AddSystemIncludeWithSubfolder(DriverArgs, CC1Args, WindowsSDKDir,
+                                      "include");
+      }
+    } else {
+      addSystemInclude(DriverArgs, CC1Args, VSDir);
     }
     return;
   }
 
   // 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",

lib/Driver/ToolChains.h

public:
 
   void
   AddClangSystemIncludeArgs(const llvm::opt::ArgList &DriverArgs,
                             llvm::opt::ArgStringList &CC1Args) const override;
   void
   AddClangCXXStdlibIncludeArgs(const llvm::opt::ArgList &DriverArgs,
                                llvm::opt::ArgStringList &CC1Args) const override;
 
+  bool getWindowsSDKDir(std::string &path, int &major, int &minor) const;
+  bool getVisualStudioInstallDir(std::string &path) const;
+  bool getVisualStudioBinariesFolder(const char *clangProgramPath,
+                                     std::string &path) const;
+
 protected:
+  void AddSystemIncludeWithSubfolder(const llvm::opt::ArgList &DriverArgs,
+                                     llvm::opt::ArgStringList &CC1Args,
+                                     const std::string &folder,
+                                     const char *subfolder) const;
+
   Tool *buildLinker() const override;
   Tool *buildAssembler() const override;
 };
 
 
 class LLVM_LIBRARY_VISIBILITY XCore : public ToolChain {
 public:
   XCore(const Driver &D, const llvm::Triple &Triple,

lib/Driver/Tools.cpp

static void addSanitizerRTWindows(const ToolChain &TC, const ArgList &Args,
                                   ArgStringList &CmdArgs,
                                   StringRef RTName) {
   SmallString<128> LibSanitizer(getCompilerRTLibDir(TC));
   llvm::sys::path::append(LibSanitizer,
                           Twine("clang_rt.") + RTName + ".lib");
   CmdArgs.push_back(Args.MakeArgString(LibSanitizer));
 }
 
+// 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 char *ClangProgramPath) {
+  const toolchains::Windows &WTC = static_cast<const toolchains::Windows &>(TC);
+  std::string visualStudioBinDir;
+  if (WTC.getVisualStudioBinariesFolder(ClangProgramPath, visualStudioBinDir)) {
+    SmallString<128> FilePath(visualStudioBinDir);
+    llvm::sys::path::append(FilePath, Exe);
+    if (llvm::sys::fs::can_execute(FilePath.c_str()))
+      return FilePath.str();
+  }
+
+  return Exe;
+}
+
 void visualstudio::Link::ConstructJob(Compilation &C, const JobAction &JA,
                                       const InputInfo &Output,
                                       const InputInfoList &Inputs,
                                       const ArgList &Args,
                                       const char *LinkingOutput) const {
   ArgStringList CmdArgs;
 
   if (Output.isFilename()) {
if (A.getOption().matches(options::OPT_l)) {
       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);
   }
 
-  const char *Exec =
-    Args.MakeArgString(getToolChain().GetProgramPath("link.exe"));
+  // 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.
+  llvm::SmallString<128> linkPath(FindVisualStudioExecutable(
+      getToolChain(), "link.exe", C.getDriver().getClangProgramPath()));
+  const char *Exec = Args.MakeArgString(linkPath);
   C.addCommand(llvm::make_unique<Command>(JA, *this, Exec, CmdArgs));
 }
 
 void visualstudio::Compile::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));
 }
 
-// Try to find FallbackName on PATH that is not identical to ClangProgramPath.
-// If one cannot be found, return FallbackName.
-// We do this special search to prevent clang-cl from falling back onto itself
-// if it's available as cl.exe on the path.
-static std::string FindFallback(const char *FallbackName,
-                                const char *ClangProgramPath) {
-  llvm::Optional<std::string> OptPath = llvm::sys::Process::GetEnv("PATH");
-  if (!OptPath.hasValue())
-    return FallbackName;
-
-  const char EnvPathSeparatorStr[] = {llvm::sys::EnvPathSeparator, '\0'};
-  SmallVector<StringRef, 8> PathSegments;
-  llvm::SplitString(OptPath.getValue(), PathSegments, EnvPathSeparatorStr);
-
-  for (size_t i = 0, e = PathSegments.size(); i != e; ++i) {
-    StringRef PathSegment = PathSegments[i];
-    if (PathSegment.empty())
-      continue;
-
-    SmallString<128> FilePath(PathSegment);
-    llvm::sys::path::append(FilePath, FallbackName);
-    if (llvm::sys::fs::can_execute(Twine(FilePath)) &&
-        !llvm::sys::fs::equivalent(Twine(FilePath), ClangProgramPath))
-      return FilePath.str();
-  }
-
-  return FallbackName;
-}
-
 std::unique_ptr<Command> visualstudio::Compile::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.
std::unique_ptr<Command> visualstudio::Compile::GetCommand(
 
   // Output filename.
   assert(Output.getType() == types::TY_Object);
   const char *Fo = Args.MakeArgString(std::string("/Fo") +
                                       Output.getFilename());
   CmdArgs.push_back(Fo);
 
   const Driver &D = getToolChain().getDriver();
-  std::string Exec = FindFallback("cl.exe", D.getClangProgramPath());
+  std::string Exec = FindVisualStudioExecutable(getToolChain(), "cl.exe",
+                                                D.getClangProgramPath());
   return llvm::make_unique<Command>(JA, *this, Args.MakeArgString(Exec),
                                     CmdArgs);
 }
 
 
 /// XCore Tools
 // We pass assemble and link construction to the xcc tool.