Index: clang/include/clang/Frontend/FrontendOptions.h
===================================================================
--- clang/include/clang/Frontend/FrontendOptions.h
+++ clang/include/clang/Frontend/FrontendOptions.h
@@ -15,6 +15,7 @@
 #include "clang/Sema/CodeCompleteOptions.h"
 #include "clang/Serialization/ModuleFileExtension.h"
 #include "llvm/ADT/StringRef.h"
+#include "llvm/Support/MemoryBuffer.h"
 #include <cassert>
 #include <map>
 #include <memory>
Index: clang/lib/Tooling/ExpandResponseFilesCompilationDatabase.cpp
===================================================================
--- clang/lib/Tooling/ExpandResponseFilesCompilationDatabase.cpp
+++ clang/lib/Tooling/ExpandResponseFilesCompilationDatabase.cpp
@@ -60,8 +60,8 @@
         continue;
       llvm::BumpPtrAllocator Alloc;
       llvm::StringSaver Saver(Alloc);
-      llvm::cl::ExpandResponseFiles(Saver, Tokenizer, Argv, false, false, *FS,
-                                    llvm::StringRef(Cmd.Directory));
+      llvm::cl::ExpandResponseFiles(Saver, Tokenizer, Argv, false, false,
+                                    llvm::StringRef(Cmd.Directory), *FS);
       // Don't assign directly, Argv aliases CommandLine.
       std::vector<std::string> ExpandedArgv(Argv.begin(), Argv.end());
       Cmd.CommandLine = std::move(ExpandedArgv);
Index: clang/tools/apinotes-test/APINotesTest.cpp
===================================================================
--- clang/tools/apinotes-test/APINotesTest.cpp
+++ clang/tools/apinotes-test/APINotesTest.cpp
@@ -8,6 +8,8 @@
 
 #include "clang/APINotes/APINotesYAMLCompiler.h"
 #include "llvm/Support/CommandLine.h"
+#include "llvm/Support/FileSystem.h"
+#include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/Signals.h"
 #include "llvm/Support/ToolOutputFile.h"
 #include "llvm/Support/WithColor.h"
Index: clang/tools/clang-offload-wrapper/ClangOffloadWrapper.cpp
===================================================================
--- clang/tools/clang-offload-wrapper/ClangOffloadWrapper.cpp
+++ clang/tools/clang-offload-wrapper/ClangOffloadWrapper.cpp
@@ -27,6 +27,7 @@
 #include "llvm/Support/Errc.h"
 #include "llvm/Support/Error.h"
 #include "llvm/Support/ErrorOr.h"
+#include "llvm/Support/FileSystem.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/Signals.h"
 #include "llvm/Support/ToolOutputFile.h"
Index: llvm/include/llvm/Support/CommandLine.h
===================================================================
--- llvm/include/llvm/Support/CommandLine.h
+++ llvm/include/llvm/Support/CommandLine.h
@@ -31,7 +31,6 @@
 #include "llvm/ADT/iterator_range.h"
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/ManagedStatic.h"
-#include "llvm/Support/VirtualFileSystem.h"
 #include "llvm/Support/raw_ostream.h"
 #include <cassert>
 #include <climits>
@@ -44,6 +43,10 @@
 
 namespace llvm {
 
+namespace vfs {
+class FileSystem;
+}
+
 class StringSaver;
 
 /// cl Namespace - This namespace contains all of the command line option
@@ -2091,11 +2094,18 @@
 /// \param [in] CurrentDir Path used to resolve relative rsp files. If set to
 /// None, process' cwd is used instead.
 /// \return true if all @files were expanded successfully or there were none.
+bool ExpandResponseFiles(StringSaver &Saver, TokenizerCallback Tokenizer,
+                         SmallVectorImpl<const char *> &Argv, bool MarkEOLs,
+                         bool RelativeNames,
+                         llvm::Optional<llvm::StringRef> CurrentDir,
+                         llvm::vfs::FileSystem &FS);
+
+/// An overload of ExpandResponseFiles() that uses
+/// llvm::vfs::getRealFileSystem().
 bool ExpandResponseFiles(
     StringSaver &Saver, TokenizerCallback Tokenizer,
     SmallVectorImpl<const char *> &Argv, bool MarkEOLs = false,
     bool RelativeNames = false,
-    llvm::vfs::FileSystem &FS = *llvm::vfs::getRealFileSystem(),
     llvm::Optional<llvm::StringRef> CurrentDir = llvm::None);
 
 /// A convenience helper which concatenates the options specified by the
Index: llvm/lib/Analysis/ModuleSummaryAnalysis.cpp
===================================================================
--- llvm/lib/Analysis/ModuleSummaryAnalysis.cpp
+++ llvm/lib/Analysis/ModuleSummaryAnalysis.cpp
@@ -50,6 +50,7 @@
 #include "llvm/Pass.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/CommandLine.h"
+#include "llvm/Support/FileSystem.h"
 #include <algorithm>
 #include <cassert>
 #include <cstdint>
Index: llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
===================================================================
--- llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
+++ llvm/lib/CodeGen/AsmPrinter/AsmPrinter.cpp
@@ -110,6 +110,7 @@
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/ErrorHandling.h"
+#include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Format.h"
 #include "llvm/Support/MathExtras.h"
 #include "llvm/Support/Path.h"
Index: llvm/lib/CodeGen/CommandFlags.cpp
===================================================================
--- llvm/lib/CodeGen/CommandFlags.cpp
+++ llvm/lib/CodeGen/CommandFlags.cpp
@@ -17,6 +17,7 @@
 #include "llvm/MC/SubtargetFeature.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Host.h"
+#include "llvm/Support/MemoryBuffer.h"
 
 using namespace llvm;
 
Index: llvm/lib/CodeGen/GlobalISel/CSEInfo.cpp
===================================================================
--- llvm/lib/CodeGen/GlobalISel/CSEInfo.cpp
+++ llvm/lib/CodeGen/GlobalISel/CSEInfo.cpp
@@ -10,6 +10,7 @@
 //===----------------------------------------------------------------------===//
 #include "llvm/CodeGen/GlobalISel/CSEInfo.h"
 #include "llvm/CodeGen/MachineRegisterInfo.h"
+#include "llvm/Support/Error.h"
 #include "llvm/InitializePasses.h"
 
 #define DEBUG_TYPE "cseinfo"
Index: llvm/lib/LTO/LTO.cpp
===================================================================
--- llvm/lib/LTO/LTO.cpp
+++ llvm/lib/LTO/LTO.cpp
@@ -35,6 +35,7 @@
 #include "llvm/Object/IRObjectFile.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Error.h"
+#include "llvm/Support/FileSystem.h"
 #include "llvm/Support/ManagedStatic.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/Path.h"
Index: llvm/lib/ProfileData/Coverage/CoverageMappingReader.cpp
===================================================================
--- llvm/lib/ProfileData/Coverage/CoverageMappingReader.cpp
+++ llvm/lib/ProfileData/Coverage/CoverageMappingReader.cpp
@@ -20,10 +20,10 @@
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/Triple.h"
 #include "llvm/Object/Binary.h"
+#include "llvm/Object/COFF.h"
 #include "llvm/Object/Error.h"
 #include "llvm/Object/MachOUniversal.h"
 #include "llvm/Object/ObjectFile.h"
-#include "llvm/Object/COFF.h"
 #include "llvm/ProfileData/InstrProf.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/Compression.h"
@@ -33,6 +33,7 @@
 #include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/LEB128.h"
 #include "llvm/Support/MathExtras.h"
+#include "llvm/Support/Path.h"
 #include "llvm/Support/raw_ostream.h"
 #include <vector>
 
Index: llvm/lib/Remarks/YAMLRemarkSerializer.cpp
===================================================================
--- llvm/lib/Remarks/YAMLRemarkSerializer.cpp
+++ llvm/lib/Remarks/YAMLRemarkSerializer.cpp
@@ -13,6 +13,7 @@
 
 #include "llvm/Remarks/YAMLRemarkSerializer.h"
 #include "llvm/Support/CommandLine.h"
+#include "llvm/Support/FileSystem.h"
 
 using namespace llvm;
 using namespace llvm::remarks;
Index: llvm/lib/Support/CommandLine.cpp
===================================================================
--- llvm/lib/Support/CommandLine.cpp
+++ llvm/lib/Support/CommandLine.cpp
@@ -1138,8 +1138,9 @@
 /// StringSaver and tokenization strategy.
 bool cl::ExpandResponseFiles(StringSaver &Saver, TokenizerCallback Tokenizer,
                              SmallVectorImpl<const char *> &Argv, bool MarkEOLs,
-                             bool RelativeNames, llvm::vfs::FileSystem &FS,
-                             llvm::Optional<llvm::StringRef> CurrentDir) {
+                             bool RelativeNames,
+                             llvm::Optional<llvm::StringRef> CurrentDir,
+                             llvm::vfs::FileSystem &FS) {
   bool AllExpanded = true;
   struct ResponseFileRecord {
     std::string File;
@@ -1247,6 +1248,15 @@
   return AllExpanded;
 }
 
+bool cl::ExpandResponseFiles(StringSaver &Saver, TokenizerCallback Tokenizer,
+                             SmallVectorImpl<const char *> &Argv, bool MarkEOLs,
+                             bool RelativeNames,
+                             llvm::Optional<StringRef> CurrentDir) {
+  return ExpandResponseFiles(Saver, std::move(Tokenizer), Argv, MarkEOLs,
+                             RelativeNames, std::move(CurrentDir),
+                             *vfs::getRealFileSystem());
+}
+
 bool cl::expandResponseFiles(int Argc, const char *const *Argv,
                              const char *EnvVar, StringSaver &Saver,
                              SmallVectorImpl<const char *> &NewArgv) {
@@ -1273,14 +1283,14 @@
   }
   if (llvm::Error Err =
           ExpandResponseFile(CfgFile, Saver, cl::tokenizeConfigFile, Argv,
-                             /*MarkEOLs*/ false, /*RelativeNames*/ true,
+                             /*MarkEOLs=*/false, /*RelativeNames=*/true,
                              *llvm::vfs::getRealFileSystem())) {
     // TODO: The error should be propagated up the stack.
     llvm::consumeError(std::move(Err));
     return false;
   }
   return ExpandResponseFiles(Saver, cl::tokenizeConfigFile, Argv,
-                             /*MarkEOLs*/ false, /*RelativeNames*/ true);
+                             /*MarkEOLs=*/false, /*RelativeNames=*/true);
 }
 
 bool cl::ParseCommandLineOptions(int argc, const char *const *argv,
Index: llvm/lib/Support/WithColor.cpp
===================================================================
--- llvm/lib/Support/WithColor.cpp
+++ llvm/lib/Support/WithColor.cpp
@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Support/WithColor.h"
+#include "llvm/Support/Error.h"
 #include "llvm/Support/CommandLine.h"
 
 using namespace llvm;
Index: llvm/lib/Transforms/Utils/Debugify.cpp
===================================================================
--- llvm/lib/Transforms/Utils/Debugify.cpp
+++ llvm/lib/Transforms/Utils/Debugify.cpp
@@ -25,6 +25,7 @@
 #include "llvm/IR/PassInstrumentation.h"
 #include "llvm/Pass.h"
 #include "llvm/Support/CommandLine.h"
+#include "llvm/Support/FileSystem.h"
 #include "llvm/Support/JSON.h"
 
 #define DEBUG_TYPE "debugify"
Index: llvm/tools/llvm-cov/TestingSupport.cpp
===================================================================
--- llvm/tools/llvm-cov/TestingSupport.cpp
+++ llvm/tools/llvm-cov/TestingSupport.cpp
@@ -10,6 +10,7 @@
 #include "llvm/ProfileData/InstrProf.h"
 #include "llvm/Support/Alignment.h"
 #include "llvm/Support/CommandLine.h"
+#include "llvm/Support/FileSystem.h"
 #include "llvm/Support/LEB128.h"
 #include "llvm/Support/raw_ostream.h"
 #include <functional>
Index: llvm/tools/llvm-cxxmap/llvm-cxxmap.cpp
===================================================================
--- llvm/tools/llvm-cxxmap/llvm-cxxmap.cpp
+++ llvm/tools/llvm-cxxmap/llvm-cxxmap.cpp
@@ -11,10 +11,11 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/CommandLine.h"
+#include "llvm/Support/FileSystem.h"
 #include "llvm/Support/InitLLVM.h"
 #include "llvm/Support/LineIterator.h"
 #include "llvm/Support/MemoryBuffer.h"
Index: llvm/tools/llvm-exegesis/llvm-exegesis.cpp
===================================================================
--- llvm/tools/llvm-exegesis/llvm-exegesis.cpp
+++ llvm/tools/llvm-exegesis/llvm-exegesis.cpp
@@ -32,6 +32,7 @@
 #include "llvm/MC/MCSubtargetInfo.h"
 #include "llvm/Object/ObjectFile.h"
 #include "llvm/Support/CommandLine.h"
+#include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Format.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/SourceMgr.h"
Index: llvm/tools/llvm-jitlink/llvm-jitlink.cpp
===================================================================
--- llvm/tools/llvm-jitlink/llvm-jitlink.cpp
+++ llvm/tools/llvm-jitlink/llvm-jitlink.cpp
@@ -37,6 +37,7 @@
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/InitLLVM.h"
 #include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Support/Path.h"
 #include "llvm/Support/Process.h"
 #include "llvm/Support/TargetRegistry.h"
 #include "llvm/Support/TargetSelect.h"
Index: llvm/tools/llvm-libtool-darwin/llvm-libtool-darwin.cpp
===================================================================
--- llvm/tools/llvm-libtool-darwin/llvm-libtool-darwin.cpp
+++ llvm/tools/llvm-libtool-darwin/llvm-libtool-darwin.cpp
@@ -21,6 +21,7 @@
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/InitLLVM.h"
 #include "llvm/Support/LineIterator.h"
+#include "llvm/Support/VirtualFileSystem.h"
 #include "llvm/Support/WithColor.h"
 #include "llvm/TextAPI/Architecture.h"
 #include <map>
Index: llvm/tools/llvm-rtdyld/llvm-rtdyld.cpp
===================================================================
--- llvm/tools/llvm-rtdyld/llvm-rtdyld.cpp
+++ llvm/tools/llvm-rtdyld/llvm-rtdyld.cpp
@@ -27,6 +27,7 @@
 #include "llvm/Object/SymbolSize.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/DynamicLibrary.h"
+#include "llvm/Support/FileSystem.h"
 #include "llvm/Support/InitLLVM.h"
 #include "llvm/Support/MSVCErrorWorkarounds.h"
 #include "llvm/Support/Memory.h"
Index: llvm/tools/split-file/split-file.cpp
===================================================================
--- llvm/tools/split-file/split-file.cpp
+++ llvm/tools/split-file/split-file.cpp
@@ -16,6 +16,7 @@
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/FileOutputBuffer.h"
+#include "llvm/Support/FileSystem.h"
 #include "llvm/Support/LineIterator.h"
 #include "llvm/Support/MemoryBuffer.h"
 #include "llvm/Support/Path.h"
Index: llvm/unittests/Support/CommandLineTest.cpp
===================================================================
--- llvm/unittests/Support/CommandLineTest.cpp
+++ llvm/unittests/Support/CommandLineTest.cpp
@@ -827,8 +827,8 @@
   llvm::BumpPtrAllocator A;
   llvm::StringSaver Saver(A);
   ASSERT_TRUE(llvm::cl::ExpandResponseFiles(
-      Saver, llvm::cl::TokenizeGNUCommandLine, Argv, false, true, FS,
-      /*CurrentDir=*/StringRef(TestRoot)));
+      Saver, llvm::cl::TokenizeGNUCommandLine, Argv, false, true,
+      /*CurrentDir=*/StringRef(TestRoot), FS));
   EXPECT_THAT(Argv, testing::Pointwise(
                         StringEquality(),
                         {"test/test", "-flag_1", "-option_1", "-option_2",
@@ -890,8 +890,8 @@
   cl::TokenizerCallback Tokenizer = cl::TokenizeGNUCommandLine;
 #endif
   ASSERT_FALSE(
-      cl::ExpandResponseFiles(Saver, Tokenizer, Argv, false, false, FS,
-                              /*CurrentDir=*/llvm::StringRef(TestRoot)));
+      cl::ExpandResponseFiles(Saver, Tokenizer, Argv, false, false,
+                              /*CurrentDir=*/llvm::StringRef(TestRoot), FS));
 
   EXPECT_THAT(Argv,
               testing::Pointwise(StringEquality(),
@@ -929,8 +929,8 @@
   BumpPtrAllocator A;
   StringSaver Saver(A);
   ASSERT_FALSE(cl::ExpandResponseFiles(Saver, cl::TokenizeGNUCommandLine, Argv,
-                                       false, false, FS,
-                                       /*CurrentDir=*/StringRef(TestRoot)));
+                                       false, false,
+                                       /*CurrentDir=*/StringRef(TestRoot), FS));
 
   // ASSERT instead of EXPECT to prevent potential out-of-bounds access.
   ASSERT_EQ(Argv.size(), 1 + NON_RSP_AT_ARGS + 2);
@@ -964,8 +964,8 @@
   BumpPtrAllocator A;
   StringSaver Saver(A);
   ASSERT_TRUE(cl::ExpandResponseFiles(Saver, cl::TokenizeGNUCommandLine, Argv,
-                                      false, true, FS,
-                                      /*CurrentDir=*/StringRef(TestRoot)));
+                                      false, true,
+                                      /*CurrentDir=*/StringRef(TestRoot), FS));
   EXPECT_THAT(Argv,
               testing::Pointwise(StringEquality(), {"test/test", "-flag"}));
 }
@@ -984,8 +984,8 @@
   BumpPtrAllocator A;
   StringSaver Saver(A);
   ASSERT_TRUE(cl::ExpandResponseFiles(Saver, cl::TokenizeWindowsCommandLine,
-                                      Argv, true, true, FS,
-                                      /*CurrentDir=*/StringRef(TestRoot)));
+                                      Argv, true, true,
+                                      /*CurrentDir=*/StringRef(TestRoot), FS));
   const char *Expected[] = {"clang", "-Xclang", "-Wno-whatever", nullptr,
                             "input.cpp"};
   ASSERT_EQ(array_lengthof(Expected), Argv.size());
Index: llvm/unittests/Transforms/Utils/ScalarEvolutionExpanderTest.cpp
===================================================================
--- llvm/unittests/Transforms/Utils/ScalarEvolutionExpanderTest.cpp
+++ llvm/unittests/Transforms/Utils/ScalarEvolutionExpanderTest.cpp
@@ -22,6 +22,7 @@
 #include "llvm/IR/Module.h"
 #include "llvm/IR/PatternMatch.h"
 #include "llvm/IR/Verifier.h"
+#include "llvm/Support/SourceMgr.h"
 #include "gtest/gtest.h"
 
 namespace llvm {
Index: llvm/unittests/tools/llvm-exegesis/X86/BenchmarkResultTest.cpp
===================================================================
--- llvm/unittests/tools/llvm-exegesis/X86/BenchmarkResultTest.cpp
+++ llvm/unittests/tools/llvm-exegesis/X86/BenchmarkResultTest.cpp
@@ -10,6 +10,7 @@
 #include "X86InstrInfo.h"
 #include "llvm/ADT/SmallString.h"
 #include "llvm/Support/Error.h"
+#include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/TargetRegistry.h"
 #include "llvm/Support/TargetSelect.h"
Index: llvm/utils/TableGen/GICombinerEmitter.cpp
===================================================================
--- llvm/utils/TableGen/GICombinerEmitter.cpp
+++ llvm/utils/TableGen/GICombinerEmitter.cpp
@@ -15,6 +15,7 @@
 #include "llvm/ADT/Statistic.h"
 #include "llvm/ADT/StringSet.h"
 #include "llvm/Support/CommandLine.h"
+#include "llvm/Support/Debug.h"
 #include "llvm/Support/ScopedPrinter.h"
 #include "llvm/Support/Timer.h"
 #include "llvm/TableGen/Error.h"