Support: Use sys::path::is_style_{posix,windows}() in a few places

Use the new sys::path::is_style_posix() and is_style_windows() in a few
places that need to detect the system's native path style.

In llvm/lib/Support/Path.cpp, this patch removes most uses of the
private `real_style()`, where is_style_posix() and is_style_windows()
are just a little tidier.

Elsewhere, this removes `_WIN32` macro checks. Added a FIXME to a
FileManagerTest that seemed fishy, but maintained the existing
behaviour.

Differential Revision: https://reviews.llvm.org/D112289

clang/include/clang/Basic/JsonSupport.h

@@ -12,6 +12,7 @@
 #include "clang/Basic/LLVM.h"
 #include "clang/Basic/SourceManager.h"
 #include "llvm/ADT/StringRef.h"
+#include "llvm/Support/Path.h"
 #include "llvm/Support/raw_ostream.h"
 #include <iterator>
 
@@ -98,18 +99,19 @@ inline void printSourceLocationAsJson(raw_ostream &Out, SourceLocation Loc,
     if (AddBraces)
       Out << "{ ";
     std::string filename(PLoc.getFilename());
-#ifdef _WIN32
-    // Remove forbidden Windows path characters
-    auto RemoveIt =
-        std::remove_if(filename.begin(), filename.end(), [](auto Char) {
-          static const char ForbiddenChars[] = "<>*?\"|";
-          return std::find(std::begin(ForbiddenChars), std::end(ForbiddenChars),
-                           Char) != std::end(ForbiddenChars);
-        });
-    filename.erase(RemoveIt, filename.end());
-    // Handle windows-specific path delimiters.
-    std::replace(filename.begin(), filename.end(), '\\', '/');
-#endif
+    if (is_style_windows(llvm::sys::path::Style::native)) {
+      // Remove forbidden Windows path characters
+      auto RemoveIt =
+          std::remove_if(filename.begin(), filename.end(), [](auto Char) {
+            static const char ForbiddenChars[] = "<>*?\"|";
+            return std::find(std::begin(ForbiddenChars),
+                             std::end(ForbiddenChars),
+                             Char) != std::end(ForbiddenChars);
+          });
+      filename.erase(RemoveIt, filename.end());
+      // Handle windows-specific path delimiters.
+      std::replace(filename.begin(), filename.end(), '\\', '/');
+    }
     Out << "\"line\": " << PLoc.getLine()
         << ", \"column\": " << PLoc.getColumn()
         << ", \"file\": \"" << filename << "\"";

clang/lib/Basic/FileManager.cpp

@@ -123,16 +123,16 @@ FileManager::getDirectoryRef(StringRef DirName, bool CacheFailure) {
       DirName != llvm::sys::path::root_path(DirName) &&
       llvm::sys::path::is_separator(DirName.back()))
     DirName = DirName.substr(0, DirName.size()-1);
-#ifdef _WIN32
-  // Fixing a problem with "clang C:test.c" on Windows.
-  // Stat("C:") does not recognize "C:" as a valid directory
-  std::string DirNameStr;
-  if (DirName.size() > 1 && DirName.back() == ':' &&
-      DirName.equals_insensitive(llvm::sys::path::root_name(DirName))) {
-    DirNameStr = DirName.str() + '.';
-    DirName = DirNameStr;
+  if (is_style_windows(llvm::sys::path::Style::native)) {
+    // Fixing a problem with "clang C:test.c" on Windows.
+    // Stat("C:") does not recognize "C:" as a valid directory
+    std::string DirNameStr;
+    if (DirName.size() > 1 && DirName.back() == ':' &&
+        DirName.equals_insensitive(llvm::sys::path::root_name(DirName))) {
+      DirNameStr = DirName.str() + '.';
+      DirName = DirNameStr;
+    }
   }
-#endif
 
   ++NumDirLookups;
 

clang/lib/Driver/Driver.cpp

@@ -4899,11 +4899,11 @@ const char *Driver::GetNamedOutputPath(Compilation &C, const JobAction &JA,
                                        bool MultipleArchs,
                                        StringRef OffloadingPrefix) const {
   std::string BoundArch = OrigBoundArch.str();
-#if defined(_WIN32)
-  // BoundArch may contains ':', which is invalid in file names on Windows,
-  // therefore replace it with '%'.
-  std::replace(BoundArch.begin(), BoundArch.end(), ':', '@');
-#endif
+  if (is_style_windows(llvm::sys::path::Style::native)) {
+    // BoundArch may contains ':', which is invalid in file names on Windows,
+    // therefore replace it with '%'.
+    std::replace(BoundArch.begin(), BoundArch.end(), ':', '@');
+  }
 
   llvm::PrettyStackTraceString CrashInfo("Computing output path");
   // Output to a user requested destination?

clang/lib/Driver/ToolChain.cpp

@@ -169,10 +169,11 @@ static const DriverSuffix *FindDriverSuffix(StringRef ProgName, size_t &Pos) {
 /// present and lower-casing the string on Windows.
 static std::string normalizeProgramName(llvm::StringRef Argv0) {
   std::string ProgName = std::string(llvm::sys::path::stem(Argv0));
-#ifdef _WIN32
-  // Transform to lowercase for case insensitive file systems.
-  std::transform(ProgName.begin(), ProgName.end(), ProgName.begin(), ::tolower);
-#endif
+  if (is_style_windows(llvm::sys::path::Style::native)) {
+    // Transform to lowercase for case insensitive file systems.
+    std::transform(ProgName.begin(), ProgName.end(), ProgName.begin(),
+                   ::tolower);
+  }
   return ProgName;
 }
 

clang/lib/Lex/PPDirectives.cpp

@@ -2012,20 +2012,16 @@ Preprocessor::ImportAction Preprocessor::HandleHeaderIncludeOrImport(
   SourceLocation FilenameLoc = FilenameTok.getLocation();
   StringRef LookupFilename = Filename;
 
-#ifdef _WIN32
-  llvm::sys::path::Style BackslashStyle = llvm::sys::path::Style::windows;
-#else
   // Normalize slashes when compiling with -fms-extensions on non-Windows. This
   // is unnecessary on Windows since the filesystem there handles backslashes.
   SmallString<128> NormalizedPath;
-  llvm::sys::path::Style BackslashStyle = llvm::sys::path::Style::posix;
-  if (LangOpts.MicrosoftExt) {
+  llvm::sys::path::Style BackslashStyle = llvm::sys::path::Style::native;
+  if (is_style_posix(BackslashStyle) && LangOpts.MicrosoftExt) {
     NormalizedPath = Filename.str();
     llvm::sys::path::native(NormalizedPath);
     LookupFilename = NormalizedPath;
     BackslashStyle = llvm::sys::path::Style::windows;
   }
-#endif
 
   Optional<FileEntryRef> File = LookupHeaderIncludeOrImport(
       CurDir, Filename, FilenameLoc, FilenameRange, FilenameTok,

clang/unittests/Basic/FileManagerTest.cpp

@@ -31,18 +31,18 @@ private:
 
   void InjectFileOrDirectory(const char *Path, ino_t INode, bool IsFile,
                              const char *StatPath) {
-#ifndef _WIN32
     SmallString<128> NormalizedPath(Path);
-    llvm::sys::path::native(NormalizedPath);
-    Path = NormalizedPath.c_str();
-
     SmallString<128> NormalizedStatPath;
-    if (StatPath) {
-      NormalizedStatPath = StatPath;
-      llvm::sys::path::native(NormalizedStatPath);
-      StatPath = NormalizedStatPath.c_str();
+    if (is_style_posix(llvm::sys::path::Style::native)) {
+      llvm::sys::path::native(NormalizedPath);
+      Path = NormalizedPath.c_str();
+
+      if (StatPath) {
+        NormalizedStatPath = StatPath;
+        llvm::sys::path::native(NormalizedStatPath);
+        StatPath = NormalizedStatPath.c_str();
+      }
     }
-#endif
 
     if (!StatPath)
       StatPath = Path;
@@ -74,11 +74,11 @@ public:
                           bool isFile,
                           std::unique_ptr<llvm::vfs::File> *F,
                           llvm::vfs::FileSystem &FS) override {
-#ifndef _WIN32
     SmallString<128> NormalizedPath(Path);
-    llvm::sys::path::native(NormalizedPath);
-    Path = NormalizedPath.c_str();
-#endif
+    if (is_style_posix(llvm::sys::path::Style::native)) {
+      llvm::sys::path::native(NormalizedPath);
+      Path = NormalizedPath.c_str();
+    }
 
     if (StatCalls.count(Path) != 0) {
       Status = StatCalls[Path];
@@ -436,13 +436,16 @@ TEST_F(FileManagerTest, getVirtualFileWithDifferentName) {
 
 #endif  // !_WIN32
 
+static StringRef getSystemRoot() {
+  return is_style_windows(llvm::sys::path::Style::native) ? "C:/" : "/";
+}
+
 TEST_F(FileManagerTest, makeAbsoluteUsesVFS) {
-  SmallString<64> CustomWorkingDir;
-#ifdef _WIN32
-  CustomWorkingDir = "C:";
-#else
-  CustomWorkingDir = "/";
-#endif
+  // FIXME: Should this be using a root path / call getSystemRoot()? For now,
+  // avoiding that and leaving the test as-is.
+  SmallString<64> CustomWorkingDir =
+      is_style_windows(llvm::sys::path::Style::native) ? StringRef("C:")
+                                                       : StringRef("/");
   llvm::sys::path::append(CustomWorkingDir, "some", "weird", "path");
 
   auto FS = IntrusiveRefCntPtr<llvm::vfs::InMemoryFileSystem>(
@@ -464,12 +467,7 @@ TEST_F(FileManagerTest, makeAbsoluteUsesVFS) {
 
 // getVirtualFile should always fill the real path.
 TEST_F(FileManagerTest, getVirtualFileFillsRealPathName) {
-  SmallString<64> CustomWorkingDir;
-#ifdef _WIN32
-  CustomWorkingDir = "C:/";
-#else
-  CustomWorkingDir = "/";
-#endif
+  SmallString<64> CustomWorkingDir = getSystemRoot();
 
   auto FS = IntrusiveRefCntPtr<llvm::vfs::InMemoryFileSystem>(
       new llvm::vfs::InMemoryFileSystem);
@@ -497,12 +495,7 @@ TEST_F(FileManagerTest, getVirtualFileFillsRealPathName) {
 }
 
 TEST_F(FileManagerTest, getFileDontOpenRealPath) {
-  SmallString<64> CustomWorkingDir;
-#ifdef _WIN32
-  CustomWorkingDir = "C:/";
-#else
-  CustomWorkingDir = "/";
-#endif
+  SmallString<64> CustomWorkingDir = getSystemRoot();
 
   auto FS = IntrusiveRefCntPtr<llvm::vfs::InMemoryFileSystem>(
       new llvm::vfs::InMemoryFileSystem);

clang/unittests/Driver/ToolChainTest.cpp

@@ -85,9 +85,8 @@ TEST(ToolChainTest, VFSGCCInstallation) {
       llvm::raw_string_ostream OS(S);
       C->getDefaultToolChain().printVerboseInfo(OS);
     }
-#if _WIN32
-    std::replace(S.begin(), S.end(), '\\', '/');
-#endif
+    if (is_style_windows(llvm::sys::path::Style::native))
+      std::replace(S.begin(), S.end(), '\\', '/');
     EXPECT_EQ(
         "Found candidate GCC installation: "
         "/usr/lib/gcc/arm-linux-gnueabihf/4.6.3\n"
@@ -110,9 +109,8 @@ TEST(ToolChainTest, VFSGCCInstallation) {
       llvm::raw_string_ostream OS(S);
       C->getDefaultToolChain().printVerboseInfo(OS);
     }
-#if _WIN32
-    std::replace(S.begin(), S.end(), '\\', '/');
-#endif
+    if (is_style_windows(llvm::sys::path::Style::native))
+      std::replace(S.begin(), S.end(), '\\', '/');
     // Test that 4.5.3 from --sysroot is not overridden by 4.6.3 (larger
     // version) from /usr.
     EXPECT_EQ("Found candidate GCC installation: "
@@ -153,9 +151,8 @@ TEST(ToolChainTest, VFSGCCInstallationRelativeDir) {
     llvm::raw_string_ostream OS(S);
     C->getDefaultToolChain().printVerboseInfo(OS);
   }
-#if _WIN32
-  std::replace(S.begin(), S.end(), '\\', '/');
-#endif
+  if (is_style_windows(llvm::sys::path::Style::windows))
+    std::replace(S.begin(), S.end(), '\\', '/');
   EXPECT_EQ("Found candidate GCC installation: "
             "/home/test/bin/../lib/gcc/arm-linux-gnueabi/4.6.1\n"
             "Selected GCC installation: "

clang/unittests/Lex/HeaderSearchTest.cpp

@@ -188,11 +188,11 @@ TEST_F(HeaderSearchTest, HeaderMapFrameworkLookup) {
 
   std::string HeaderDirName = "/tmp/Sources/Foo/Headers/";
   std::string HeaderName = "Foo.h";
-#ifdef _WIN32
-  // Force header path to be absolute on windows.
-  // As headermap content should represent absolute locations.
-  HeaderDirName = "C:" + HeaderDirName;
-#endif /*_WIN32*/
+  if (is_style_windows(llvm::sys::path::Style::native)) {
+    // Force header path to be absolute on windows.
+    // As headermap content should represent absolute locations.
+    HeaderDirName = "C:" + HeaderDirName;
+  }
 
   test::HMapFileMockMaker<FileTy> Maker(File);
   auto a = Maker.addString("Foo/Foo.h");

clang/unittests/Tooling/RefactoringTest.cpp

@@ -1031,18 +1031,17 @@ TEST_F(MergeReplacementsTest, OverlappingRanges) {
       toReplacements({{"", 0, 3, "cc"}, {"", 3, 3, "dd"}}));
 }
 
+static constexpr bool usesWindowsPaths() {
+  return is_style_windows(llvm::sys::path::Style::native);
+}
+
 TEST(DeduplicateByFileTest, PathsWithDots) {
   std::map<std::string, Replacements> FileToReplaces;
   llvm::IntrusiveRefCntPtr<llvm::vfs::InMemoryFileSystem> VFS(
       new llvm::vfs::InMemoryFileSystem());
   FileManager FileMgr(FileSystemOptions(), VFS);
-#if !defined(_WIN32)
-  StringRef Path1 = "a/b/.././c.h";
-  StringRef Path2 = "a/c.h";
-#else
-  StringRef Path1 = "a\\b\\..\\.\\c.h";
-  StringRef Path2 = "a\\c.h";
-#endif
+  StringRef Path1 = usesWindowsPaths() ? "a\\b\\..\\.\\c.h" : "a/b/.././c.h";
+  StringRef Path2 = usesWindowsPaths() ? "a\\c.h" : "a/c.h";
   EXPECT_TRUE(VFS->addFile(Path1, 0, llvm::MemoryBuffer::getMemBuffer("")));
   EXPECT_TRUE(VFS->addFile(Path2, 0, llvm::MemoryBuffer::getMemBuffer("")));
   FileToReplaces[std::string(Path1)] = Replacements();
@@ -1057,13 +1056,8 @@ TEST(DeduplicateByFileTest, PathWithDotSlash) {
   llvm::IntrusiveRefCntPtr<llvm::vfs::InMemoryFileSystem> VFS(
       new llvm::vfs::InMemoryFileSystem());
   FileManager FileMgr(FileSystemOptions(), VFS);
-#if !defined(_WIN32)
-  StringRef Path1 = "./a/b/c.h";
-  StringRef Path2 = "a/b/c.h";
-#else
-  StringRef Path1 = ".\\a\\b\\c.h";
-  StringRef Path2 = "a\\b\\c.h";
-#endif
+  StringRef Path1 = usesWindowsPaths() ? ".\\a\\b\\c.h" : "./a/b/c.h";
+  StringRef Path2 = usesWindowsPaths() ? "a\\b\\c.h" : "a/b/c.h";
   EXPECT_TRUE(VFS->addFile(Path1, 0, llvm::MemoryBuffer::getMemBuffer("")));
   EXPECT_TRUE(VFS->addFile(Path2, 0, llvm::MemoryBuffer::getMemBuffer("")));
   FileToReplaces[std::string(Path1)] = Replacements();
@@ -1078,13 +1072,8 @@ TEST(DeduplicateByFileTest, NonExistingFilePath) {
   llvm::IntrusiveRefCntPtr<llvm::vfs::InMemoryFileSystem> VFS(
       new llvm::vfs::InMemoryFileSystem());
   FileManager FileMgr(FileSystemOptions(), VFS);
-#if !defined(_WIN32)
-  StringRef Path1 = "./a/b/c.h";
-  StringRef Path2 = "a/b/c.h";
-#else
-  StringRef Path1 = ".\\a\\b\\c.h";
-  StringRef Path2 = "a\\b\\c.h";
-#endif
+  StringRef Path1 = usesWindowsPaths() ? ".\\a\\b\\c.h" : "./a/b/c.h";
+  StringRef Path2 = usesWindowsPaths() ? "a\\b\\c.h" : "a/b/c.h";
   FileToReplaces[std::string(Path1)] = Replacements();
   FileToReplaces[std::string(Path2)] = Replacements();
   FileToReplaces = groupReplacementsByFile(FileMgr, FileToReplaces);

llvm/include/llvm/Support/VirtualFileSystem.h

@@ -788,12 +788,7 @@ private:
   /// Whether to perform case-sensitive comparisons.
   ///
   /// Currently, case-insensitive matching only works correctly with ASCII.
-  bool CaseSensitive =
-#ifdef _WIN32
-      false;
-#else
-      true;
-#endif
+  bool CaseSensitive = is_style_posix(sys::path::Style::native);
 
   /// IsRelativeOverlay marks whether a ExternalContentsPrefixDir path must
   /// be prefixed in every 'external-contents' when reading from YAML files.

llvm/lib/Support/GraphWriter.cpp

@@ -23,11 +23,12 @@
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/ErrorOr.h"
 #include "llvm/Support/FileSystem.h"
+#include "llvm/Support/Path.h"
 #include "llvm/Support/Program.h"
 #include "llvm/Support/raw_ostream.h"
 #include <cassert>
-#include <system_error>
 #include <string>
+#include <system_error>
 #include <vector>
 
 using namespace llvm;
@@ -94,11 +95,8 @@ StringRef llvm::DOT::getColorString(unsigned ColorNumber) {
 
 static std::string replaceIllegalFilenameChars(std::string Filename,
                                                const char ReplacementChar) {
-#ifdef _WIN32
-  std::string IllegalChars = "\\/:?\"<>|";
-#else
-  std::string IllegalChars = "/";
-#endif
+  std::string IllegalChars =
+      is_style_windows(sys::path::Style::native) ? "\\/:?\"<>|" : "/";
 
   for (char IllegalChar : IllegalChars) {
     std::replace(Filename.begin(), Filename.end(), IllegalChar,

llvm/lib/Support/Path.cpp

@@ -64,7 +64,7 @@ namespace {
     if (path.empty())
       return path;
 
-    if (real_style(style) == Style::windows) {
+    if (is_style_windows(style)) {
       // C:
       if (path.size() >= 2 &&
           std::isalpha(static_cast<unsigned char>(path[0])) && path[1] == ':')
@@ -96,7 +96,7 @@ namespace {
 
     size_t pos = str.find_last_of(separators(style), str.size() - 1);
 
-    if (real_style(style) == Style::windows) {
+    if (is_style_windows(style)) {
       if (pos == StringRef::npos)
         pos = str.find_last_of(':', str.size() - 2);
     }
@@ -111,7 +111,7 @@ namespace {
   // directory in str, it returns StringRef::npos.
   size_t root_dir_start(StringRef str, Style style) {
     // case "c:/"
-    if (real_style(style) == Style::windows) {
+    if (is_style_windows(style)) {
       if (str.size() > 2 && str[1] == ':' && is_separator(str[2], style))
         return 2;
     }
@@ -257,7 +257,7 @@ const_iterator &const_iterator::operator++() {
     // Root dir.
     if (was_net ||
         // c:/
-        (real_style(S) == Style::windows && Component.endswith(":"))) {
+        (is_style_windows(S) && Component.endswith(":"))) {
       Component = Path.substr(Position, 1);
       return *this;
     }
@@ -346,7 +346,7 @@ StringRef root_path(StringRef path, Style style) {
   if (b != e) {
     bool has_net =
         b->size() > 2 && is_separator((*b)[0], style) && (*b)[1] == (*b)[0];
-    bool has_drive = (real_style(style) == Style::windows) && b->endswith(":");
+    bool has_drive = is_style_windows(style) && b->endswith(":");
 
     if (has_net || has_drive) {
       if ((++pos != e) && is_separator((*pos)[0], style)) {
@@ -371,7 +371,7 @@ StringRef root_name(StringRef path, Style style) {
   if (b != e) {
     bool has_net =
         b->size() > 2 && is_separator((*b)[0], style) && (*b)[1] == (*b)[0];
-    bool has_drive = (real_style(style) == Style::windows) && b->endswith(":");
+    bool has_drive = is_style_windows(style) && b->endswith(":");
 
     if (has_net || has_drive) {
       // just {C:,//net}, return the first component.
@@ -388,7 +388,7 @@ StringRef root_directory(StringRef path, Style style) {
   if (b != e) {
     bool has_net =
         b->size() > 2 && is_separator((*b)[0], style) && (*b)[1] == (*b)[0];
-    bool has_drive = (real_style(style) == Style::windows) && b->endswith(":");
+    bool has_drive = is_style_windows(style) && b->endswith(":");
 
     if ((has_net || has_drive) &&
         // {C:,//net}, skip to the next component.
@@ -495,7 +495,7 @@ void replace_extension(SmallVectorImpl<char> &path, const Twine &extension,
 static bool starts_with(StringRef Path, StringRef Prefix,
                         Style style = Style::native) {
   // Windows prefix matching : case and separator insensitive
-  if (real_style(style) == Style::windows) {
+  if (is_style_windows(style)) {
     if (Path.size() < Prefix.size())
       return false;
     for (size_t I = 0, E = Prefix.size(); I != E; ++I) {
@@ -546,7 +546,7 @@ void native(const Twine &path, SmallVectorImpl<char> &result, Style style) {
 void native(SmallVectorImpl<char> &Path, Style style) {
   if (Path.empty())
     return;
-  if (real_style(style) == Style::windows) {
+  if (is_style_windows(style)) {
     std::replace(Path.begin(), Path.end(), '/', '\\');
     if (Path[0] == '~' && (Path.size() == 1 || is_separator(Path[1], style))) {
       SmallString<128> PathHome;
@@ -560,7 +560,7 @@ void native(SmallVectorImpl<char> &Path, Style style) {
 }
 
 std::string convert_to_slash(StringRef path, Style style) {
-  if (real_style(style) != Style::windows)
+  if (is_style_posix(style))
     return std::string(path);
 
   std::string s = path.str();
@@ -595,13 +595,13 @@ StringRef extension(StringRef path, Style style) {
 bool is_separator(char value, Style style) {
   if (value == '/')
     return true;
-  if (real_style(style) == Style::windows)
+  if (is_style_windows(style))
     return value == '\\';
   return false;
 }
 
 StringRef get_separator(Style style) {
-  if (real_style(style) == Style::windows)
+  if (is_style_windows(style))
     return "\\";
   return "/";
 }
@@ -667,8 +667,7 @@ bool is_absolute(const Twine &path, Style style) {
   StringRef p = path.toStringRef(path_storage);
 
   bool rootDir = has_root_directory(p, style);
-  bool rootName =
-      (real_style(style) != Style::windows) || has_root_name(p, style);
+  bool rootName = is_style_posix(style) || has_root_name(p, style);
 
   return rootDir && rootName;
 }
@@ -682,7 +681,7 @@ bool is_absolute_gnu(const Twine &path, Style style) {
   if (!p.empty() && is_separator(p.front(), style))
     return true;
 
-  if (real_style(style) == Style::windows) {
+  if (is_style_windows(style)) {
     // Handle drive letter pattern (a character followed by ':') on Windows.
     if (p.size() >= 2 && (p[0] && p[1] == ':'))
       return true;
@@ -902,8 +901,7 @@ void make_absolute(const Twine &current_directory,
   bool rootName = path::has_root_name(p);
 
   // Already absolute.
-  if ((rootName || real_style(Style::native) != Style::windows) &&
-      rootDirectory)
+  if ((rootName || is_style_posix(Style::native)) && rootDirectory)
     return;
 
   // All of the following conditions will need the current directory.

llvm/tools/lli/lli.cpp

@@ -355,13 +355,12 @@ private:
       return false;
 
     std::string CacheSubdir = ModID.substr(PrefixLength);
-#if defined(_WIN32)
-    // Transform "X:\foo" => "/X\foo" for convenience.
-    if (isalpha(CacheSubdir[0]) && CacheSubdir[1] == ':') {
+    // Transform "X:\foo" => "/X\foo" for convenience on Windows.
+    if (is_style_windows(llvm::sys::path::Style::native) &&
+        isalpha(CacheSubdir[0]) && CacheSubdir[1] == ':') {
       CacheSubdir[1] = CacheSubdir[0];
       CacheSubdir[0] = '/';
     }
-#endif
 
     CacheName = CacheDir + CacheSubdir;
     size_t pos = CacheName.rfind('.');