[Driver] Use UniversalCRT on Windows if available

[ikudrin]

Summary

With Visual Studio 2015 release, a part of runtime library was extracted and now comes with Windows Kits. This patch enables clang to use Universal CRT library if %INCLUDE or %LIB environment varaibles are not specified.

See also https://llvm.org/bugs/show_bug.cgi?id=24741

[rnk]

FYI @ruiu is moving this code to LLVM in D12604.

lib/Driver/MSVCToolChain.cpp

328–340

Refactor this into a helper like StringRef getWindowsSDKArch(llvm::Triple::Arch) and share it with getWindowsSDKLibraryPath.

lib/Driver/Tools.cpp

8956–8959

Does this have to be conditional on the version of the CRT in use? If I install VS 2013 and the ucrt and am trying to use the 2013 CRT, this will put both on the libpath. Is that a problem?

[ikudrin]

• Extracted a function to convert an architecture type to a library subfolder name.
• Added a method to check if we should use Universal CRT depending on the chosen version of Visual Studio.

[ikudrin]

Just added more context to the patch.

[ikudrin]

In D12695#243320, @rnk wrote:

FYI @ruiu is moving this code to LLVM in D12604.

Thanks. I think I'll move my changes to the new place when he's finished.

[rnk]

There's a bunch of whitespace issues that clang-format can resolve. We also have the convention that variables are StudlyCaps, which isn't followed in a few places.

Do you need someone to commit this for you? If so, I can patch this in, test it manually, and deal with the style stuff if you deal with the VSDir part.

lib/Driver/MSVCToolChain.cpp

293

This should really take VSDir as a parameter instead of recomputing it, since all the callers are already computing it.

[ikudrin]

In D12695#243552, @rnk wrote:

There's a bunch of whitespace issues that clang-format can resolve.

Thanks! I'll reformat it.

We also have the convention that variables are StudlyCaps, which isn't followed in a few places.

I've tried to follow the style of the source file. Do you think I should force this rule here?

Do you need someone to commit this for you? If so, I can patch this in, test it manually, and deal with the style stuff if you deal with the VSDir part.

I'd really appreciate it. I'll prepare a new version in a few minutes.

[ikudrin]

• Fixed formatting issues.
• Normalized VariableNames.
• Reworked the useUniversalCRT method to receive a path of Visual Studio.

[ruiu]

I'm sorry about leave D12604 hanging. I didn't notice that it got a new review message. Don't mind my patch -- please just submit when you got LGTM

lib/Driver/MSVCToolChain.cpp

 #endif // USE_WIN32
 }
 
+// Convert LLVM's ArchType
+// to the corresponding name of Windows SDK libraries subfolder
+static StringRef getWindowsSDKArch(llvm::Triple::ArchType arch) {
+  switch (arch) {
+  case llvm::Triple::x86:
+    return "x86";
+  case llvm::Triple::x86_64:
+    return "x64";
+  case llvm::Triple::arm:
+    return "arm";
+  default:
+    return "";
+  }
+}
+
 /// \brief Get Windows SDK installation directory.
 bool MSVCToolChain::getWindowsSDKDir(std::string &path, int &major,
                                      int &minor) const {

     if (!found)
       return false;
 
-    llvm::sys::path::append(libPath, "um");
-    switch (getArch()) {
-    case llvm::Triple::x86:
-      llvm::sys::path::append(libPath, "x86");
-      break;
-    case llvm::Triple::x86_64:
-      llvm::sys::path::append(libPath, "x64");
-      break;
-    case llvm::Triple::arm:
-      llvm::sys::path::append(libPath, "arm");
-      break;
-    default:
+    const StringRef archName = getWindowsSDKArch(getArch());
+    if (archName.empty())
       return false;
-    }
+    llvm::sys::path::append(libPath, "um", archName);
+  }
+
+  path = libPath.str();
+  return true;
+}
+
+// Check if the Include path of a chosen version of Visual Studio contains
+// specific header files. If not, they are probably shipped with Universal CRT.
+bool clang::driver::toolchains::MSVCToolChain::useUniversalCRT() const
+{
+  std::string VSDir;
+  if (!getVisualStudioInstallDir(VSDir))
+    return false;
+
+  llvm::SmallString<128> testPath(VSDir);
+  llvm::sys::path::append(testPath, "VC\\include\\stdlib.h");
+
+  return !llvm::sys::fs::exists(testPath);
+}
+
+bool MSVCToolChain::getUniversalCRTSdkDir(std::string &path,
+                                          std::string &ucrtVersion) const
+{
+  // 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;
+
+  ucrtVersion.clear();
+
+  // Find the most recent version of Universal CRT.
+  // vcvarsqueryregistry.bat sorts entries in the include directory by names and
+  // uses the last one of the list.
+  // So we compare entry names lexicographically to find the greatest one.
+  std::error_code ec;
+  llvm::SmallString<128> includePath(path);
+  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 name = llvm::sys::path::filename(dirIt->path());
+    if (name > ucrtVersion)
+      ucrtVersion = name;
   }
 
+  return !ucrtVersion.empty();
+}
+
+bool MSVCToolChain::getUniversalCRTLibraryPath(std::string &path) const
+{
+  std::string universalCRTSdkPath;
+  std::string ucrtVersion;
+
+  path.clear();
+  if (!getUniversalCRTSdkDir(universalCRTSdkPath, ucrtVersion))
+    return false;
+
+  StringRef archName = getWindowsSDKArch(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;
 }

   if (getVisualStudioInstallDir(VSDir)) {
     AddSystemIncludeWithSubfolder(DriverArgs, CC1Args, VSDir, "VC\\include");
 
+    if (useUniversalCRT()) {
+      std::string universalCRTSdkPath;
+      std::string ucrtVersion;
+      if (getUniversalCRTSdkDir(universalCRTSdkPath, ucrtVersion)) {
+        llvm::SmallString<128> ucrtIncludePath(universalCRTSdkPath);
+        llvm::sys::path::append(ucrtIncludePath,
+                                "Include", ucrtVersion, "ucrt");
+        addSystemInclude(DriverArgs, CC1Args, ucrtIncludePath);
+      }
+    }
+
     std::string WindowsSDKDir;
     int major, minor;
     if (getWindowsSDKDir(WindowsSDKDir, major, minor)) {

lib/Driver/ToolChains.h

 
   bool getWindowsSDKDir(std::string &path, int &major, int &minor) const;
   bool getWindowsSDKLibraryPath(std::string &path) const;
+  /// \brief Check if Universal CRT should be used if available
+  bool useUniversalCRT() const;
+  bool getUniversalCRTSdkDir(std::string &path,
+                        std::string &ucrtVersion) const;
+  bool getUniversalCRTLibraryPath(std::string &path) const;
   bool getVisualStudioInstallDir(std::string &path) const;
   bool getVisualStudioBinariesFolder(const char *clangProgramPath,
                                      std::string &path) const;

lib/Driver/Tools.cpp

           Args.MakeArgString(std::string("-libpath:") + LibDir.c_str()));
     }
 
+    if (MSVC.useUniversalCRT()) {
+      std::string UniversalCRTLibPath;
+      if (MSVC.getUniversalCRTLibraryPath(UniversalCRTLibPath))
+        CmdArgs.push_back(Args.MakeArgString(std::string("-libpath:") +
+                                             UniversalCRTLibPath.c_str()));
+    }
+
     std::string WindowsSdkLibPath;
     if (MSVC.getWindowsSDKLibraryPath(WindowsSdkLibPath))
       CmdArgs.push_back(Args.MakeArgString(std::string("-libpath:") +