Index: include/clang/Driver/Job.h
===================================================================
--- include/clang/Driver/Job.h
+++ include/clang/Driver/Job.h
@@ -17,6 +17,7 @@
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/iterator.h"
 #include "llvm/Option/Option.h"
+#include "llvm/Support/Path.h"
 #include <memory>
 #include <string>
 #include <utility>
@@ -95,8 +96,10 @@
   Command(const Command &) = default;
   virtual ~Command() = default;
 
-  virtual void Print(llvm::raw_ostream &OS, const char *Terminator, bool Quote,
-                     CrashReportInfo *CrashInfo = nullptr) const;
+  virtual void Print(
+      llvm::raw_ostream &OS, const char *Terminator, bool Quote,
+      CrashReportInfo *CrashInfo = nullptr,
+      llvm::sys::path::Style PathStyle = llvm::sys::path::Style::native) const;
 
   virtual int Execute(ArrayRef<Optional<StringRef>> Redirects,
                       std::string *ErrMsg, bool *ExecutionFailed) const;
@@ -127,7 +130,9 @@
   const llvm::opt::ArgStringList &getArguments() const { return Arguments; }
 
   /// Print a command argument, and optionally quote it.
-  static void printArg(llvm::raw_ostream &OS, StringRef Arg, bool Quote);
+  static void
+  printArg(llvm::raw_ostream &OS, StringRef Arg, bool Quote,
+           llvm::sys::path::Style PathStyle = llvm::sys::path::Style::native);
 };
 
 /// Like Command, but with a fallback which is executed in case
@@ -140,7 +145,9 @@
                   std::unique_ptr<Command> Fallback_);
 
   void Print(llvm::raw_ostream &OS, const char *Terminator, bool Quote,
-             CrashReportInfo *CrashInfo = nullptr) const override;
+             CrashReportInfo *CrashInfo = nullptr,
+             llvm::sys::path::Style PathStyle =
+                 llvm::sys::path::Style::native) const override;
 
   int Execute(ArrayRef<Optional<StringRef>> Redirects, std::string *ErrMsg,
               bool *ExecutionFailed) const override;
@@ -157,7 +164,9 @@
                       ArrayRef<InputInfo> Inputs);
 
   void Print(llvm::raw_ostream &OS, const char *Terminator, bool Quote,
-             CrashReportInfo *CrashInfo = nullptr) const override;
+             CrashReportInfo *CrashInfo = nullptr,
+             llvm::sys::path::Style PathStyle =
+                 llvm::sys::path::Style::native) const override;
 
   int Execute(ArrayRef<Optional<StringRef>> Redirects, std::string *ErrMsg,
               bool *ExecutionFailed) const override;
Index: lib/Driver/Compilation.cpp
===================================================================
--- lib/Driver/Compilation.cpp
+++ lib/Driver/Compilation.cpp
@@ -174,7 +174,12 @@
     if (getDriver().CCPrintOptions)
       *OS << "[Logging clang options]";
 
-    C.Print(*OS, "\n", /*Quote=*/getDriver().CCPrintOptions);
+    llvm::Triple TT(llvm::Triple::normalize(getDriver().getTargetTriple()));
+    llvm::sys::path::Style PathStyle = TT.isOSCygMing()
+                                           ? llvm::sys::path::Style::posix
+                                           : llvm::sys::path::Style::native;
+    C.Print(*OS, "\n", /*Quote=*/getDriver().CCPrintOptions, nullptr,
+            PathStyle);
 
     if (OS != &llvm::errs())
       delete OS;
Index: lib/Driver/Job.cpp
===================================================================
--- lib/Driver/Job.cpp
+++ lib/Driver/Job.cpp
@@ -98,7 +98,13 @@
   return false;
 }
 
-void Command::printArg(raw_ostream &OS, StringRef Arg, bool Quote) {
+void Command::printArg(raw_ostream &OS, StringRef Arg, bool Quote,
+                       llvm::sys::path::Style PathStyle) {
+  std::string Buf;
+  if (PathStyle == llvm::sys::path::Style::posix) {
+    Buf = llvm::sys::path::convert_to_slash(Arg);
+    Arg = Buf;
+  }
   const bool Escape = Arg.find_first_of("\"\\$") != StringRef::npos;
 
   if (!Quote && !Escape) {
@@ -212,10 +218,11 @@
 }
 
 void Command::Print(raw_ostream &OS, const char *Terminator, bool Quote,
-                    CrashReportInfo *CrashInfo) const {
+                    CrashReportInfo *CrashInfo,
+                    llvm::sys::path::Style PathStyle) const {
   // Always quote the exe.
   OS << ' ';
-  printArg(OS, Executable, /*Quote=*/true);
+  printArg(OS, Executable, /*Quote=*/true, PathStyle);
 
   ArrayRef<const char *> Args = Arguments;
   SmallVector<const char *, 128> ArgsRespFile;
@@ -263,14 +270,14 @@
     }
 
     OS << ' ';
-    printArg(OS, Arg, Quote);
+    printArg(OS, Arg, Quote, PathStyle);
   }
 
   if (CrashInfo && HaveCrashVFS) {
     OS << ' ';
-    printArg(OS, "-ivfsoverlay", Quote);
+    printArg(OS, "-ivfsoverlay", Quote, PathStyle);
     OS << ' ';
-    printArg(OS, CrashInfo->VFSPath.str(), Quote);
+    printArg(OS, CrashInfo->VFSPath.str(), Quote, PathStyle);
 
     // The leftover modules from the crash are stored in
     //  <name>.cache/vfs/modules
@@ -285,7 +292,7 @@
     ModCachePath.append(RelModCacheDir.c_str());
 
     OS << ' ';
-    printArg(OS, ModCachePath, Quote);
+    printArg(OS, ModCachePath, Quote, PathStyle);
   }
 
   if (ResponseFile != nullptr) {
@@ -372,11 +379,12 @@
     : Command(Source_, Creator_, Executable_, Arguments_, Inputs),
       Fallback(std::move(Fallback_)) {}
 
-void FallbackCommand::Print(raw_ostream &OS, const char *Terminator,
-                            bool Quote, CrashReportInfo *CrashInfo) const {
-  Command::Print(OS, "", Quote, CrashInfo);
+void FallbackCommand::Print(raw_ostream &OS, const char *Terminator, bool Quote,
+                            CrashReportInfo *CrashInfo,
+                            llvm::sys::path::Style PathStyle) const {
+  Command::Print(OS, "", Quote, CrashInfo, PathStyle);
   OS << " ||";
-  Fallback->Print(OS, Terminator, Quote, CrashInfo);
+  Fallback->Print(OS, Terminator, Quote, CrashInfo, PathStyle);
 }
 
 static bool ShouldFallback(int ExitCode) {
@@ -413,7 +421,8 @@
     : Command(Source_, Creator_, Executable_, Arguments_, Inputs) {}
 
 void ForceSuccessCommand::Print(raw_ostream &OS, const char *Terminator,
-                            bool Quote, CrashReportInfo *CrashInfo) const {
+                                bool Quote, CrashReportInfo *CrashInfo,
+                                llvm::sys::path::Style PathStyle) const {
   Command::Print(OS, "", Quote, CrashInfo);
   OS << " || (exit 0)" << Terminator;
 }