diff --git a/clang/include/clang/Basic/DiagnosticDriverKinds.td b/clang/include/clang/Basic/DiagnosticDriverKinds.td
index c6e6eaf47cc9..ce455ae9768a 100644
--- a/clang/include/clang/Basic/DiagnosticDriverKinds.td
+++ b/clang/include/clang/Basic/DiagnosticDriverKinds.td
@@ -98,6 +98,20 @@ def err_drv_unknown_argument : Error<"unknown argument: '%0'">;
 def warn_drv_unknown_argument_clang_cl : Warning<
   "unknown argument ignored in clang-cl: '%0'">,
   InGroup<UnknownArgument>;
+
+def warn_drv_ycyu_no_arg_clang_cl : Warning<
+  "support for '%0' without a filename not implemented yet; flag ignored">,
+  InGroup<ClangClPch>;
+def warn_drv_ycyu_different_arg_clang_cl : Warning<
+  "support for '/Yc' and '/Yu' with different filenames not implemented yet; flags ignored">,
+  InGroup<ClangClPch>;
+def warn_drv_ycyu_no_fi_arg_clang_cl : Warning<
+  "support for '%0' without a corresponding /FI flag not implemented yet; flag ignored">,
+  InGroup<ClangClPch>;
+def warn_drv_yc_multiple_inputs_clang_cl : Warning<
+  "support for '/Yc' with more than one source file not implemented yet; flag ignored">,
+  InGroup<ClangClPch>;
+
 def err_drv_invalid_value : Error<"invalid value '%1' in '%0'">;
 def err_drv_invalid_int_value : Error<"invalid integral value '%1' in '%0'">;
 def err_drv_invalid_remap_file : Error<
diff --git a/clang/include/clang/Basic/DiagnosticGroups.td b/clang/include/clang/Basic/DiagnosticGroups.td
index 969050df5963..e5d8794b555f 100644
--- a/clang/include/clang/Basic/DiagnosticGroups.td
+++ b/clang/include/clang/Basic/DiagnosticGroups.td
@@ -785,6 +785,8 @@ def Microsoft : DiagGroup<"microsoft",
      MicrosoftConstInit, MicrosoftVoidPseudoDtor, MicrosoftAnonTag,
      MicrosoftCommentPaste, MicrosoftEndOfFile]>;
 
+def ClangClPch : DiagGroup<"clang-cl-pch">;
+
 def ObjCNonUnifiedException : DiagGroup<"objc-nonunified-exceptions">;
 
 def ObjCProtocolMethodImpl : DiagGroup<"objc-protocol-method-implementation">;
diff --git a/clang/include/clang/Driver/CC1Options.td b/clang/include/clang/Driver/CC1Options.td
index d6905db96252..66a8acf2c688 100644
--- a/clang/include/clang/Driver/CC1Options.td
+++ b/clang/include/clang/Driver/CC1Options.td
@@ -495,6 +495,10 @@ def fixit_to_temp : Flag<["-"], "fixit-to-temporary">,
 
 def foverride_record_layout_EQ : Joined<["-"], "foverride-record-layout=">,
   HelpText<"Override record layouts with those in the given file">;
+def find_pch_source_EQ : Joined<["-"], "find-pch-source=">,
+  HelpText<"When building a pch, try to find the input file in include "
+           "directories, as if it had been included by the argument passed "
+           "to this flag.">;
   
 //===----------------------------------------------------------------------===//
 // Language Options
diff --git a/clang/include/clang/Driver/CLCompatOptions.td b/clang/include/clang/Driver/CLCompatOptions.td
index dbd25f572331..d7c84134e246 100644
--- a/clang/include/clang/Driver/CLCompatOptions.td
+++ b/clang/include/clang/Driver/CLCompatOptions.td
@@ -20,6 +20,9 @@ def cl_compile_Group : OptionGroup<"<clang-cl compile-only options>">,
 def cl_ignored_Group : OptionGroup<"<clang-cl ignored options>">,
   Group<cl_Group>;
 
+def cl_internal_Group : OptionGroup<"<clang-cl internal options>">,
+  Group<cl_Group>;
+
 class CLFlag<string name> : Option<["/", "-"], name, KIND_FLAG>,
   Group<cl_Group>, Flags<[CLOption, DriverOption]>;
 
@@ -29,6 +32,9 @@ class CLCompileFlag<string name> : Option<["/", "-"], name, KIND_FLAG>,
 class CLIgnoredFlag<string name> : Option<["/", "-"], name, KIND_FLAG>,
   Group<cl_ignored_Group>, Flags<[CLOption, DriverOption, HelpHidden]>;
 
+class CLInternalFlag<string name> : Option<["-"], name, KIND_FLAG>,
+  Group<cl_internal_Group>, Flags<[CLOption, DriverOption, HelpHidden]>;
+
 class CLJoined<string name> : Option<["/", "-"], name, KIND_JOINED>,
   Group<cl_Group>, Flags<[CLOption, DriverOption]>;
 
@@ -252,6 +258,23 @@ def _SLASH_volatile_ms  : Option<["/", "-"], "volatile:ms", KIND_FLAG>,
 def _SLASH_Zl : CLFlag<"Zl">,
   HelpText<"Don't mention any default libraries in the object file">;
 
+def _SLASH_Yc : CLJoined<"Yc">,
+  HelpText<"Generate a pch file for all code up to and including <filename>">,
+  MetaVarName<"<filename>">;
+def _SLASH_Yu : CLJoined<"Yu">,
+  HelpText<"Load a pch file and use it instead of all code up to "
+           "and including <filename>">,
+  MetaVarName<"<filename>">;
+def _SLASH_Y_ : CLFlag<"Y-">,
+  HelpText<"Disable precompiled headers, overrides /Yc and /Yu">;
+def _SLASH_Fp : CLJoined<"Fp">,
+  HelpText<"Set pch filename (with /Yc and /Yu)">, MetaVarName<"<filename>">;
+
+// Internal:
+// FIXME: Once /Yc support is stable enough, turn it on by default (when /Yc
+// is passed) and remove this flag.
+def _SLASH_internal_enable_pch : CLInternalFlag<"internal-enable-pch">;
+
 // Ignored:
 
 def _SLASH_analyze_ : CLIgnoredFlag<"analyze-">;
@@ -294,7 +317,6 @@ def _SLASH_favor : CLJoined<"favor">;
 def _SLASH_FC : CLFlag<"FC">;
 def _SLASH_F : CLFlag<"F">;
 def _SLASH_Fm : CLJoined<"Fm">;
-def _SLASH_Fp : CLJoined<"Fp">;
 def _SLASH_Fr : CLJoined<"Fr">;
 def _SLASH_FR : CLJoined<"FR">;
 def _SLASH_FU : CLJoinedOrSeparate<"FU">;
@@ -332,11 +354,8 @@ def _SLASH_V : CLFlag<"V">;
 def _SLASH_WL : CLFlag<"WL">;
 def _SLASH_Wp64 : CLFlag<"Wp64">;
 def _SLASH_X : CLFlag<"X">;
-def _SLASH_Yc : CLJoined<"Yc">;
-def _SLASH_Y_ : CLFlag<"Y-">;
 def _SLASH_Yd : CLFlag<"Yd">;
 def _SLASH_Yl : CLJoined<"Yl">;
-def _SLASH_Yu : CLJoined<"Yu">;
 def _SLASH_Za : CLFlag<"Za">;
 def _SLASH_Zc : CLJoined<"Zc:">;
 def _SLASH_Ze : CLFlag<"Ze">;
diff --git a/clang/include/clang/Driver/Driver.h b/clang/include/clang/Driver/Driver.h
index ccf23e046962..f0924946e849 100644
--- a/clang/include/clang/Driver/Driver.h
+++ b/clang/include/clang/Driver/Driver.h
@@ -423,6 +423,9 @@ public:
   /// GCC goes to extra lengths here to be a bit more robust.
   std::string GetTemporaryPath(StringRef Prefix, const char *Suffix) const;
 
+  /// Return the pathname of the pch file in clang-cl mode.
+  std::string GetClPchPath(Compilation &C, StringRef BaseName) const;
+
   /// ShouldUseClangCompiler - Should the clang compiler be used to
   /// handle this action.
   bool ShouldUseClangCompiler(const JobAction &JA) const;
diff --git a/clang/include/clang/Driver/Job.h b/clang/include/clang/Driver/Job.h
index 263356f396f3..3366fc48d711 100644
--- a/clang/include/clang/Driver/Job.h
+++ b/clang/include/clang/Driver/Job.h
@@ -138,6 +138,20 @@ private:
   std::unique_ptr<Command> Fallback;
 };
 
+/// Like Command, but always pretends that the wrapped command succeeded.
+class ForceSuccessCommand : public Command {
+public:
+  ForceSuccessCommand(const Action &Source_, const Tool &Creator_,
+                      const char *Executable_, const ArgStringList &Arguments_,
+                      ArrayRef<InputInfo> Inputs);
+
+  void Print(llvm::raw_ostream &OS, const char *Terminator, bool Quote,
+             CrashReportInfo *CrashInfo = nullptr) const override;
+
+  int Execute(const StringRef **Redirects, std::string *ErrMsg,
+              bool *ExecutionFailed) const override;
+};
+
 /// JobList - A sequence of jobs to perform.
 class JobList {
 public:
diff --git a/clang/include/clang/Frontend/CompilerInstance.h b/clang/include/clang/Frontend/CompilerInstance.h
index 83eed2cdc592..fe36eeee2e66 100644
--- a/clang/include/clang/Frontend/CompilerInstance.h
+++ b/clang/include/clang/Frontend/CompilerInstance.h
@@ -748,10 +748,11 @@ public:
   ///
   /// \return True on success.
   static bool InitializeSourceManager(const FrontendInputFile &Input,
-                DiagnosticsEngine &Diags,
-                FileManager &FileMgr,
-                SourceManager &SourceMgr,
-                const FrontendOptions &Opts);
+                                      DiagnosticsEngine &Diags,
+                                      FileManager &FileMgr,
+                                      SourceManager &SourceMgr,
+                                      HeaderSearch *HS,
+                                      const FrontendOptions &Opts);
 
   /// }
 
diff --git a/clang/include/clang/Frontend/FrontendOptions.h b/clang/include/clang/Frontend/FrontendOptions.h
index c800a5148e49..71c08ec9c63f 100644
--- a/clang/include/clang/Frontend/FrontendOptions.h
+++ b/clang/include/clang/Frontend/FrontendOptions.h
@@ -266,6 +266,10 @@ public:
   /// \brief Auxiliary triple for CUDA compilation.
   std::string AuxTriple;
 
+  /// \brief If non-empty, search the pch input file as it was a header
+  // included by this file.
+  std::string FindPchSource;
+
 public:
   FrontendOptions() :
     DisableFree(false), RelocatablePCH(false), ShowHelp(false),
diff --git a/clang/lib/Driver/Driver.cpp b/clang/lib/Driver/Driver.cpp
index eaf29de2aaf1..8965d3d6c3c5 100644
--- a/clang/lib/Driver/Driver.cpp
+++ b/clang/lib/Driver/Driver.cpp
@@ -1452,6 +1452,66 @@ void Driver::BuildActions(Compilation &C, DerivedArgList &Args,
     }
   }
 
+  // Diagnose unsupported forms of /Yc /Yu. Ignore /Yc/Yu for now if:
+  // * no filename after it
+  // * both /Yc and /Yu passed but with different filenames
+  // * corresponding file not also passed as /FI
+  Arg *YcArg = Args.getLastArg(options::OPT__SLASH_Yc);
+  Arg *YuArg = Args.getLastArg(options::OPT__SLASH_Yu);
+  if (YcArg && YcArg->getValue()[0] == '\0') {
+    Diag(clang::diag::warn_drv_ycyu_no_arg_clang_cl) << YcArg->getSpelling();
+    Args.eraseArg(options::OPT__SLASH_Yc);
+    YcArg = nullptr;
+  }
+  if (YuArg && YuArg->getValue()[0] == '\0') {
+    Diag(clang::diag::warn_drv_ycyu_no_arg_clang_cl) << YuArg->getSpelling();
+    Args.eraseArg(options::OPT__SLASH_Yu);
+    YuArg = nullptr;
+  }
+  if (YcArg && YuArg && strcmp(YcArg->getValue(), YuArg->getValue()) != 0) {
+    Diag(clang::diag::warn_drv_ycyu_different_arg_clang_cl);
+    Args.eraseArg(options::OPT__SLASH_Yc);
+    Args.eraseArg(options::OPT__SLASH_Yu);
+    YcArg = YuArg = nullptr;
+  }
+  if (YcArg || YuArg) {
+    StringRef Val = YcArg ? YcArg->getValue() : YuArg->getValue();
+    bool FoundMatchingInclude = false;
+    for (const Arg *Inc : Args.filtered(options::OPT_include)) {
+      // FIXME: Do case-insensitive matching and consider / and \ as equal.
+      if (Inc->getValue() == Val)
+        FoundMatchingInclude = true;
+    }
+    if (!FoundMatchingInclude) {
+      Diag(clang::diag::warn_drv_ycyu_no_fi_arg_clang_cl)
+          << (YcArg ? YcArg : YuArg)->getSpelling();
+      Args.eraseArg(options::OPT__SLASH_Yc);
+      Args.eraseArg(options::OPT__SLASH_Yu);
+      YcArg = YuArg = nullptr;
+    }
+  }
+  if (YcArg && Inputs.size() > 1) {
+    Diag(clang::diag::warn_drv_yc_multiple_inputs_clang_cl);
+    Args.eraseArg(options::OPT__SLASH_Yc);
+    YcArg = nullptr;
+  }
+  if (Args.hasArg(options::OPT__SLASH_Y_)) {
+    // /Y- disables all pch handling.  Rather than check for it everywhere,
+    // just remove clang-cl pch-related flags here.
+    Args.eraseArg(options::OPT__SLASH_Fp);
+    Args.eraseArg(options::OPT__SLASH_Yc);
+    Args.eraseArg(options::OPT__SLASH_Yu);
+    YcArg = YuArg = nullptr;
+  }
+  // FIXME: For now, only enable pch support if an internal flag is passed too.
+  // Remove this once pch support has stabilitzed.
+  if (!Args.hasArg(options::OPT__SLASH_internal_enable_pch)) {
+    Args.eraseArg(options::OPT__SLASH_Fp);
+    Args.eraseArg(options::OPT__SLASH_Yc);
+    Args.eraseArg(options::OPT__SLASH_Yu);
+    YcArg = YuArg = nullptr;
+  }
+
   // Construct the actions to perform.
   ActionList LinkerInputs;
 
@@ -1463,6 +1523,25 @@ void Driver::BuildActions(Compilation &C, DerivedArgList &Args,
     PL.clear();
     types::getCompilationPhases(InputType, PL);
 
+    if (YcArg) {
+      // Add a separate precompile phase for the compile phase.
+      if (FinalPhase >= phases::Compile) {
+        llvm::SmallVector<phases::ID, phases::MaxNumberOfPhases> PCHPL;
+        types::getCompilationPhases(types::TY_CXXHeader, PCHPL);
+        Arg *PchInputArg = MakeInputArg(Args, Opts, YcArg->getValue());
+
+        // Build the pipeline for the pch file.
+        Action *ClangClPch = C.MakeAction<InputAction>(*PchInputArg, InputType);
+        for (phases::ID Phase : PCHPL)
+          ClangClPch = ConstructPhaseAction(C, Args, Phase, ClangClPch);
+        assert(ClangClPch);
+        Actions.push_back(ClangClPch);
+        // The driver currently exits after the first failed command.  This
+        // relies on that behavior, to make sure if the pch generation fails,
+        // the main compilation won't run.
+      }
+    }
+
     // If the first step comes after the final phase we are doing as part of
     // this compilation, warn the user about it.
     phases::ID InitialPhase = PL[0];
@@ -2109,8 +2188,11 @@ const char *Driver::GetNamedOutputPath(Compilation &C, const JobAction &JA,
       Output += "-";
       Output.append(BoundArch);
       NamedOutput = C.getArgs().MakeArgString(Output.c_str());
-    } else
+    } else {
       NamedOutput = getDefaultImageName();
+    }
+  } else if (JA.getType() == types::TY_PCH && IsCLMode()) {
+    NamedOutput = C.getArgs().MakeArgString(GetClPchPath(C, BaseName).c_str());
   } else {
     const char *Suffix = types::getTypeTempSuffix(JA.getType(), IsCLMode());
     assert(Suffix && "All types used for output should have a suffix.");
@@ -2276,6 +2358,25 @@ std::string Driver::GetTemporaryPath(StringRef Prefix,
   return Path.str();
 }
 
+std::string Driver::GetClPchPath(Compilation &C, StringRef BaseName) const {
+  SmallString<128> Output;
+  if (Arg *FpArg = C.getArgs().getLastArg(options::OPT__SLASH_Fp)) {
+    // FIXME: If anybody needs it, implement this obscure rule:
+    // "If you specify a directory without a file name, the default file name
+    // is VCx0.pch., where x is the major version of Visual C++ in use."
+    Output = FpArg->getValue();
+
+    // "If you do not specify an extension as part of the path name, an
+    // extension of .pch is assumed. "
+    if (!llvm::sys::path::has_extension(Output))
+      Output += ".pch";
+  } else {
+    Output = BaseName;
+    llvm::sys::path::replace_extension(Output, ".pch");
+  }
+  return Output.str();
+}
+
 const ToolChain &Driver::getToolChain(const ArgList &Args,
                                       const llvm::Triple &Target) const {
 
diff --git a/clang/lib/Driver/Job.cpp b/clang/lib/Driver/Job.cpp
index 22904e5398a0..3eb23c9ee4c9 100644
--- a/clang/lib/Driver/Job.cpp
+++ b/clang/lib/Driver/Job.cpp
@@ -297,6 +297,29 @@ int FallbackCommand::Execute(const StringRef **Redirects, std::string *ErrMsg,
   return SecondaryStatus;
 }
 
+ForceSuccessCommand::ForceSuccessCommand(const Action &Source_,
+                                         const Tool &Creator_,
+                                         const char *Executable_,
+                                         const ArgStringList &Arguments_,
+                                         ArrayRef<InputInfo> Inputs)
+    : Command(Source_, Creator_, Executable_, Arguments_, Inputs) {}
+
+void ForceSuccessCommand::Print(raw_ostream &OS, const char *Terminator,
+                            bool Quote, CrashReportInfo *CrashInfo) const {
+  Command::Print(OS, "", Quote, CrashInfo);
+  OS << " || (exit 0)" << Terminator;
+}
+
+int ForceSuccessCommand::Execute(const StringRef **Redirects,
+                                 std::string *ErrMsg,
+                                 bool *ExecutionFailed) const {
+  int Status = Command::Execute(Redirects, ErrMsg, ExecutionFailed);
+  (void)Status;
+  if (ExecutionFailed)
+    *ExecutionFailed = false;
+  return 0;
+}
+
 void JobList::Print(raw_ostream &OS, const char *Terminator, bool Quote,
                     CrashReportInfo *CrashInfo) const {
   for (const auto &Job : *this)
diff --git a/clang/lib/Driver/Tools.cpp b/clang/lib/Driver/Tools.cpp
index a0fceb9672af..0f5c700ce616 100644
--- a/clang/lib/Driver/Tools.cpp
+++ b/clang/lib/Driver/Tools.cpp
@@ -386,9 +386,71 @@ void Clang::AddPreprocessingOptions(Compilation &C, const JobAction &JA,
   // wonky, but we include looking for .gch so we can support seamless
   // replacement into a build system already set up to be generating
   // .gch files.
+  int YcIndex = -1, YuIndex = -1;
+  {
+    int AI = -1;
+    const Arg *YcArg = Args.getLastArg(options::OPT__SLASH_Yc);
+    const Arg *YuArg = Args.getLastArg(options::OPT__SLASH_Yu);
+    for (const Arg *A : Args.filtered(options::OPT_clang_i_Group)) {
+      // Walk the whole i_Group and skip non "-include" flags so that the index
+      // here matches the index in the next loop below.
+      ++AI;
+      if (!A->getOption().matches(options::OPT_include))
+        continue;
+      if (YcArg && strcmp(A->getValue(), YcArg->getValue()) == 0)
+        YcIndex = AI;
+      if (YuArg && strcmp(A->getValue(), YuArg->getValue()) == 0)
+        YuIndex = AI;
+    }
+  }
+  if (isa<PrecompileJobAction>(JA) && YcIndex != -1) {
+    Driver::InputList Inputs;
+    D.BuildInputs(getToolChain(), C.getArgs(), Inputs);
+    assert(Inputs.size() == 1 && "Need one input when building pch");
+    CmdArgs.push_back(Args.MakeArgString(Twine("-find-pch-source=") +
+                                         Inputs[0].second->getValue()));
+  }
+
   bool RenderedImplicitInclude = false;
+  int AI = -1;
   for (const Arg *A : Args.filtered(options::OPT_clang_i_Group)) {
-    if (A->getOption().matches(options::OPT_include)) {
+    ++AI;
+
+    if (getToolChain().getDriver().IsCLMode()) {
+      // In clang-cl mode, /Ycfoo.h means that all code up to a foo.h 
+      // include is compiled into foo.h, and everything after goes into
+      // the .obj file. /Yufoo.h means that all includes prior to and including
+      // foo.h are completely skipped and replaced with a use of the pch file
+      // for foo.h.  (Each flag can have at most one value, multiple /Yc flags
+      // just mean that the last one wins.)  If /Yc and /Yu are both present
+      // and refer to the same file, /Yc wins.
+      // Note that OPT__SLASH_FI gets mapped to OPT_include.
+      // FIXME: The code here assumes that /Yc and /Yu refer to the same file.
+      // cl.exe seems to support both flags with different values, but that
+      // seems strange (which flag does /Fp now refer to?), so don't implement
+      // that until someone needs that.
+      int PchIndex = YcIndex != -1 ? YcIndex : YuIndex;
+      if (PchIndex != -1) {
+        if (isa<PrecompileJobAction>(JA)) {
+          // When building the pch, skip all includes after the pch.
+          assert(YcIndex != -1 && PchIndex == YcIndex);
+          if (AI >= YcIndex)
+            continue;
+        } else {
+          // When using the pch, skip all includes prior to the pch.
+          if (AI < PchIndex)
+            continue;
+          if (AI == PchIndex) {
+            A->claim();
+            CmdArgs.push_back("-include-pch");
+            CmdArgs.push_back(
+                Args.MakeArgString(D.GetClPchPath(C, A->getValue())));
+            continue;
+          }
+        }
+      }
+    } else if (A->getOption().matches(options::OPT_include)) {
+      // Handling of gcc-style gch precompiled headers.
       bool IsFirstImplicitInclude = !RenderedImplicitInclude;
       RenderedImplicitInclude = true;
 
@@ -5654,6 +5716,12 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
         getCLFallback()->GetCommand(C, JA, Output, Inputs, Args, LinkingOutput);
     C.addCommand(llvm::make_unique<FallbackCommand>(
         JA, *this, Exec, CmdArgs, Inputs, std::move(CLCommand)));
+  } else if (Args.hasArg(options::OPT__SLASH_fallback) &&
+             isa<PrecompileJobAction>(JA)) {
+    // In /fallback builds, run the main compilation even if the pch generation
+    // fails, so that the main compilation's fallback to cl.exe runs.
+    C.addCommand(llvm::make_unique<ForceSuccessCommand>(JA, *this, Exec,
+                                                        CmdArgs, Inputs));
   } else {
     C.addCommand(llvm::make_unique<Command>(JA, *this, Exec, CmdArgs, Inputs));
   }
diff --git a/clang/lib/Frontend/CompilerInstance.cpp b/clang/lib/Frontend/CompilerInstance.cpp
index 04a4c7dbe685..c02eb7610414 100644
--- a/clang/lib/Frontend/CompilerInstance.cpp
+++ b/clang/lib/Frontend/CompilerInstance.cpp
@@ -712,15 +712,18 @@ std::unique_ptr<llvm::raw_pwrite_stream> CompilerInstance::createOutputFile(
 // Initialization Utilities
 
 bool CompilerInstance::InitializeSourceManager(const FrontendInputFile &Input){
-  return InitializeSourceManager(Input, getDiagnostics(),
-                                 getFileManager(), getSourceManager(), 
-                                 getFrontendOpts());
+  return InitializeSourceManager(
+      Input, getDiagnostics(), getFileManager(), getSourceManager(),
+      hasPreprocessor() ? &getPreprocessor().getHeaderSearchInfo() : nullptr,
+      getFrontendOpts());
 }
 
+// static
 bool CompilerInstance::InitializeSourceManager(const FrontendInputFile &Input,
                                                DiagnosticsEngine &Diags,
                                                FileManager &FileMgr,
                                                SourceManager &SourceMgr,
+                                               HeaderSearch *HS,
                                                const FrontendOptions &Opts) {
   SrcMgr::CharacteristicKind
     Kind = Input.isSystem() ? SrcMgr::C_System : SrcMgr::C_User;
@@ -737,7 +740,32 @@ bool CompilerInstance::InitializeSourceManager(const FrontendInputFile &Input,
 
   // Figure out where to get and map in the main file.
   if (InputFile != "-") {
-    const FileEntry *File = FileMgr.getFile(InputFile, /*OpenFile=*/true);
+    const FileEntry *File;
+    if (Opts.FindPchSource.empty()) {
+      File = FileMgr.getFile(InputFile, /*OpenFile=*/true);
+    } else {
+      // When building a pch file in clang-cl mode, the .h file is built as if
+      // it was included by a cc file.  Since the driver doesn't know about
+      // all include search directories, the frontend must search the input
+      // file through HeaderSearch here, as if it had been included by the
+      // cc file at Opts.FindPchSource.
+      const FileEntry *FindFile = FileMgr.getFile(Opts.FindPchSource);
+      if (!FindFile) {
+        Diags.Report(diag::err_fe_error_reading) << Opts.FindPchSource;
+        return false;
+      }
+      const DirectoryLookup *UnusedCurDir;
+      SmallVector<std::pair<const FileEntry *, const DirectoryEntry *>, 16>
+          Includers;
+      Includers.push_back(std::make_pair(FindFile, FindFile->getDir()));
+      File = HS->LookupFile(InputFile, SourceLocation(), /*isAngled=*/false,
+                            /*FromDir=*/nullptr,
+                            /*CurDir=*/UnusedCurDir, Includers,
+                            /*SearchPath=*/nullptr,
+                            /*RelativePath=*/nullptr,
+                            /*RequestingModule=*/nullptr,
+                            /*SuggestedModule=*/nullptr, /*SkipCache=*/true);
+    }
     if (!File) {
       Diags.Report(diag::err_fe_error_reading) << InputFile;
       return false;
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index b23eb3543757..9bb33e7a7669 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -1107,6 +1107,7 @@ static InputKind ParseFrontendArgs(FrontendOptions &Opts, ArgList &Args,
     = Args.getLastArgValue(OPT_foverride_record_layout_EQ);
   Opts.AuxTriple =
       llvm::Triple::normalize(Args.getLastArgValue(OPT_aux_triple));
+  Opts.FindPchSource = Args.getLastArgValue(OPT_find_pch_source_EQ);
 
   if (const Arg *A = Args.getLastArg(OPT_arcmt_check,
                                      OPT_arcmt_modify,
diff --git a/clang/test/Driver/Inputs/pchfile.cpp b/clang/test/Driver/Inputs/pchfile.cpp
new file mode 100644
index 000000000000..e69de29bb2d1
diff --git a/clang/test/Driver/Inputs/pchfile.h b/clang/test/Driver/Inputs/pchfile.h
new file mode 100644
index 000000000000..1aafaeebe810
--- /dev/null
+++ b/clang/test/Driver/Inputs/pchfile.h
@@ -0,0 +1,3 @@
+#if defined(ERR_HEADER)
+#error nope1
+#endif
diff --git a/clang/test/Driver/cl-pch-errorhandling.cpp b/clang/test/Driver/cl-pch-errorhandling.cpp
new file mode 100644
index 000000000000..1d239c1268dd
--- /dev/null
+++ b/clang/test/Driver/cl-pch-errorhandling.cpp
@@ -0,0 +1,15 @@
+// Note: %s and %S must be preceded by --, otherwise it may be interpreted as a
+// command-line option, e.g. on Mac where %s is commonly under /Users.
+
+// /Yc but pch generation fails => main file not compiled
+// This is a separate file since executing this failure path requires
+// code generation, which makes this test require an x86 backend.
+// REQUIRES: x86-registered-target
+
+// RUN: not %clang_cl -internal-enable-pch -Werror /Yc%S/Inputs/pchfile.h /FI%S/Inputs/pchfile.h /c -DERR_HEADER -- %s 2>&1 \
+// RUN:   | FileCheck %s
+
+// CHECK: nope1
+// CHECK-NOT: nope2
+
+#error nope2
diff --git a/clang/test/Driver/cl-pch-search.cpp b/clang/test/Driver/cl-pch-search.cpp
new file mode 100644
index 000000000000..b215fd7e21f5
--- /dev/null
+++ b/clang/test/Driver/cl-pch-search.cpp
@@ -0,0 +1,6 @@
+// Note: %s and %S must be preceded by --, otherwise it may be interpreted as a
+// command-line option, e.g. on Mac where %s is commonly under /Users.
+
+// REQUIRES: x86-registered-target
+// Check that pchfile.h next to to pchfile.cc is found correctly.
+// RUN: %clang_cl -internal-enable-pch -Werror /Ycpchfile.h /FIpchfile.h /c /Fo%t.obj /Fp%t.pch -- %S/Inputs/pchfile.cpp 
diff --git a/clang/test/Driver/cl-pch.c b/clang/test/Driver/cl-pch.c
new file mode 100644
index 000000000000..df00fff2c4df
--- /dev/null
+++ b/clang/test/Driver/cl-pch.c
@@ -0,0 +1,45 @@
+// Note: %s and %S must be preceded by --, otherwise it may be interpreted as a
+// command-line option, e.g. on Mac where %s is commonly under /Users.
+
+// The main test for clang-cl pch handling is cl-pch.cpp.  This file only checks
+// a few things for .c inputs.
+
+// /Yc with a .c file should build a c pch file.
+// RUN: %clang_cl -internal-enable-pch -Werror /Ycpchfile.h /FIpchfile.h /c -### -- %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-YC %s
+// CHECK-YC: cc1
+// CHECK-YC: -emit-pch
+// CHECK-YC: -o
+// CHECK-YC: pchfile.pch
+// CHECK-YC: -x
+// CHECK-YC: "c"
+
+// But not if /TP changes the input language to C++.
+// RUN: %clang_cl /TP -internal-enable-pch -Werror /Ycpchfile.h /FIpchfile.h /c -### -- %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-YCTP %s
+// CHECK-YCTP: cc1
+// CHECK-YCTP: -emit-pch
+// CHECK-YCTP: -o
+// CHECK-YCTP: pchfile.pch
+// CHECK-YCTP: -x
+// CHECK-YCTP: "c++"
+
+// Except if a later /TC changes it back.
+// RUN: %clang_cl -internal-enable-pch -Werror /Ycpchfile.h /FIpchfile.h /c -### -- %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-YCTPTC %s
+// CHECK-YCTPTC: cc1
+// CHECK-YCTPTC: -emit-pch
+// CHECK-YCTPTC: -o
+// CHECK-YCTPTC: pchfile.pch
+// CHECK-YCTPTC: -x
+// CHECK-YCTPTC: "c"
+
+// Also check lower-case /Tp flag.
+// RUN: %clang_cl -internal-enable-pch -Werror /Tp%s /Ycpchfile.h /FIpchfile.h /c -### 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-YCTp %s
+// CHECK-YCTp: cc1
+// CHECK-YCTp: -emit-pch
+// CHECK-YCTp: -o
+// CHECK-YCTp: pchfile.pch
+// CHECK-YCTp: -x
+// CHECK-YCTp: "c++"
diff --git a/clang/test/Driver/cl-pch.cpp b/clang/test/Driver/cl-pch.cpp
new file mode 100644
index 000000000000..f415794064b3
--- /dev/null
+++ b/clang/test/Driver/cl-pch.cpp
@@ -0,0 +1,309 @@
+// Note: %s and %S must be preceded by --, otherwise it may be interpreted as a
+// command-line option, e.g. on Mac where %s is commonly under /Users.
+
+// /Yc
+// RUN: %clang_cl -internal-enable-pch -Werror /Ycpchfile.h /FIpchfile.h /c -### -- %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-YC %s
+// 1. Build .pch file.
+// CHECK-YC: cc1
+// CHECK-YC: -emit-pch
+// CHECK-YC: -o
+// CHECK-YC: pchfile.pch
+// CHECK-YC: -x
+// CHECK-YC: "c++"
+// 2. Use .pch file.
+// CHECK-YC: cc1
+// CHECK-YC: -emit-obj
+// CHECK-YC: -include-pch
+// CHECK-YC: pchfile.pch
+
+// /Yc /Fo
+// /Fo overrides the .obj output filename, but not the .pch filename
+// RUN: %clang_cl -internal-enable-pch -Werror /Fomyobj.obj /Ycpchfile.h /FIpchfile.h /c -### -- %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-YCO %s
+// 1. Build .pch file.
+// CHECK-YCO: cc1
+// CHECK-YCO: -emit-pch
+// CHECK-YCO: -o
+// CHECK-YCO: pchfile.pch
+// 2. Use .pch file.
+// CHECK-YCO: cc1
+// CHECK-YCO: -emit-obj
+// CHECK-YCO: -include-pch
+// CHECK-YCO: pchfile.pch
+// CHECK-YCO: -o
+// CHECK-YCO: myobj.obj
+
+// /Yc /Y-
+// /Y- disables pch generation
+// RUN: %clang_cl -internal-enable-pch -Werror /Y- /Ycpchfile.h /FIpchfile.h /c -### -- %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-YC-Y_ %s
+// CHECK-YC-Y_-NOT: -emit-pch
+// CHECK-YC-Y_-NOT: -include-pch
+
+// /Yu
+// RUN: %clang_cl -internal-enable-pch -Werror /Yupchfile.h /FIpchfile.h /c -### -- %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-YU %s
+// Use .pch file, but don't build it.
+// CHECK-YU-NOT: -emit-pch
+// CHECK-YU: cc1
+// CHECK-YU: -emit-obj
+// CHECK-YU: -include-pch
+// CHECK-YU: pchfile.pch
+
+// /Yu /Y-
+// RUN: %clang_cl -internal-enable-pch -Werror /Y- /Yupchfile.h /FIpchfile.h /c -### -- %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-YU-Y_ %s
+// CHECK-YU-Y_-NOT: -emit-pch
+// CHECK-YU-Y_-NOT: -include-pch
+
+// /Yc /Yu -- /Yc overrides /Yc if they both refer to the same file
+// RUN: %clang_cl -internal-enable-pch -Werror /Ycpchfile.h /Yupchfile.h /FIpchfile.h /c -### -- %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-YC-YU %s
+// 1. Build .pch file.
+// CHECK-YC-YU: cc1
+// CHECK-YC-YU: -emit-pch
+// CHECK-YC-YU: -o
+// CHECK-YC-YU: pchfile.pch
+// 2. Use .pch file.
+// CHECK-YC-YU: cc1
+// CHECK-YC-YU: -emit-obj
+// CHECK-YC-YU: -include-pch
+// CHECK-YC-YU: pchfile.pch
+
+// If /Yc /Yu refer to different files, semantics are pretty wonky.  Since this
+// doesn't seem like something that's important in practice, just punt for now.
+// RUN: %clang_cl -internal-enable-pch -Werror /Ycfoo1.h /Yufoo2.h /FIfoo1.h /FIfoo2.h /c -### -- %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-YC-YU-MISMATCH %s
+// CHECK-YC-YU-MISMATCH: error: support for '/Yc' and '/Yu' with different filenames not implemented yet; flags ignored
+
+// Similarly, punt on /Yc with more than one input file.
+// RUN: %clang_cl -internal-enable-pch -Werror /Ycfoo1.h /FIfoo1.h /c -### -- %s %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-YC-MULTIINPUT %s
+// CHECK-YC-MULTIINPUT: error: support for '/Yc' with more than one source file not implemented yet; flag ignored
+
+// /Yc /Yu /Y-
+// RUN: %clang_cl -internal-enable-pch -Werror /Ycpchfile.h /Yupchfile.h /FIpchfile.h /Y- /c -### -- %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-YC-YU-Y_ %s
+// CHECK-YC-YU-Y_-NOT: -emit-pch
+// CHECK-YC-YU-Y_-NOT: -include-pch
+
+// Test computation of pch filename in various cases.
+
+// /Yu /Fpout.pch => out.pch is filename
+// RUN: %clang_cl -internal-enable-pch -Werror /Yupchfile.h /FIpchfile.h /Fpout.pch /c -### -- %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-YUFP1 %s
+// Use .pch file, but don't build it.
+// CHECK-YUFP1: -include-pch
+// CHECK-YUFP1: out.pch
+
+// /Yu /Fpout => out.pch is filename (.pch gets added if no extension present)
+// RUN: %clang_cl -internal-enable-pch -Werror /Yupchfile.h /FIpchfile.h /Fpout.pch /c -### -- %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-YUFP2 %s
+// Use .pch file, but don't build it.
+// CHECK-YUFP2: -include-pch
+// CHECK-YUFP2: out.pch
+
+// /Yu /Fpout.bmp => out.bmp is filename (.pch not added when extension present)
+// RUN: %clang_cl -internal-enable-pch -Werror /Yupchfile.h /FIpchfile.h /Fpout.bmp /c -### -- %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-YUFP3 %s
+// Use .pch file, but don't build it.
+// CHECK-YUFP3: -include-pch
+// CHECK-YUFP3: out.bmp
+
+// /Yusub/dir.h => sub/dir.pch
+// RUN: %clang_cl -internal-enable-pch -Werror /Yusub/pchfile.h /FIsub/pchfile.h /c -### -- %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-YUFP4 %s
+// Use .pch file, but don't build it.
+// CHECK-YUFP4: -include-pch
+// CHECK-YUFP4: sub/pchfile.pch
+
+// /Yudir.h /Isub => dir.pch
+// RUN: %clang_cl -internal-enable-pch -Werror /Yupchfile.h /FIpchfile.h /Isub /c -### -- %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-YUFP5 %s
+// Use .pch file, but don't build it.
+// CHECK-YUFP5: -include-pch
+// CHECK-YUFP5: pchfile.pch
+
+// FIXME: /Fpdir: use dir/VCx0.pch when dir is directory, where x is major MSVS
+// version in use.
+
+// Spot-check one use of /Fp with /Yc too, else trust the /Yu test cases above
+// also all assume to /Yc.
+// RUN: %clang_cl -internal-enable-pch -Werror /Ycpchfile.h /FIpchfile.h /Fpsub/file.pch /c -### -- %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-YCFP %s
+// 1. Build .pch file.
+// CHECK-YCFP: cc1
+// CHECK-YCFP: -emit-pch
+// CHECK-YCFP: -o
+// CHECK-YCFP: sub/file.pch
+// 2. Use .pch file.
+// CHECK-YCFP: cc1
+// CHECK-YCFP: -emit-obj
+// CHECK-YCFP: -include-pch
+// CHECK-YCFP: sub/file.pch
+
+// /Ycfoo2.h /FIfoo1.h /FIfoo2.h /FIfoo3.h
+// => foo1 and foo2 go into pch, foo3 into main compilation
+// /Yc
+// RUN: %clang_cl -internal-enable-pch -Werror /Ycfoo2.h /FIfoo1.h /FIfoo2.h /FIfoo3.h /c -### -- %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-YCFIFIFI %s
+// 1. Build .pch file: Includes foo1.h (but NOT foo3.h) and compiles foo2.h
+// CHECK-YCFIFIFI: cc1
+// CHECK-YCFIFIFI: -emit-pch
+// CHECK-YCFIFIFI: -include
+// CHECK-YCFIFIFI: foo1.h
+// CHECK-YCFIFIFI-NOT: foo2.h
+// CHECK-YCFIFIFI-NOT: foo3.h
+// CHECK-YCFIFIFI: -o
+// CHECK-YCFIFIFI: foo2.pch
+// CHECK-YCFIFIFI: -x
+// CHECK-YCFIFIFI: "c++"
+// CHECK-YCFIFIFI: foo2.h
+// 2. Use .pch file: Inlucdes foo2.pch and foo3.h
+// CHECK-YCFIFIFI: cc1
+// CHECK-YCFIFIFI: -emit-obj
+// CHECK-YCFIFIFI-NOT: foo1.h
+// CHECK-YCFIFIFI-NOT: foo2.h
+// CHECK-YCFIFIFI: -include-pch
+// CHECK-YCFIFIFI: foo2.pch
+// CHECK-YCFIFIFI: -include
+// CHECK-YCFIFIFI: foo3.h
+
+// /Yucfoo2.h /FIfoo1.h /FIfoo2.h /FIfoo3.h
+// => foo1 foo2 filtered out, foo3 into main compilation
+// RUN: %clang_cl -internal-enable-pch -Werror /Yufoo2.h /FIfoo1.h /FIfoo2.h /FIfoo3.h /c -### -- %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-YUFIFIFI %s
+// Use .pch file, but don't build it.
+// CHECK-YUFIFIFI-NOT: -emit-pch
+// CHECK-YUFIFIFI: cc1
+// CHECK-YUFIFIFI: -emit-obj
+// CHECK-YUFIFIFI-NOT: foo1.h
+// CHECK-YUFIFIFI-NOT: foo2.h
+// CHECK-YUFIFIFI: -include-pch
+// CHECK-YUFIFIFI: foo2.pch
+// CHECK-YUFIFIFI: -include
+// CHECK-YUFIFIFI: foo3.h
+
+// FIXME: Implement support for /Ycfoo.h / /Yufoo.h without /FIfoo.h
+// RUN: %clang_cl -internal-enable-pch -Werror /Ycfoo.h /c -### -- %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-YC-NOFI %s
+// CHECK-YC-NOFI: error: support for '/Yc' without a corresponding /FI flag not implemented yet; flag ignored
+// RUN: %clang_cl -internal-enable-pch -Werror /Yufoo.h /c -### -- %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-YU-NOFI %s
+// CHECK-YU-NOFI: error: support for '/Yu' without a corresponding /FI flag not implemented yet; flag ignored
+
+// /Yc and /FI relative to /I paths...
+// The rules are:
+// Yu/Yc and FI parameter must match exactly, else it's not found
+// Must match literally exactly: /FI./foo.h /Ycfoo.h does _not_ work.
+// However, the path can be relative to /I paths.
+// FIXME: Update the error messages below once /FI is no longer required, but
+// these test cases all should stay failures as they fail with cl.exe.
+
+// Check that ./ isn't canonicalized away.
+// RUN: %clang_cl -internal-enable-pch -Werror /Ycpchfile.h /FI./pchfile.h /c -### -- %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-YC-I1 %s
+// CHECK-YC-I1: support for '/Yc' without a corresponding /FI flag not implemented yet; flag ignored
+
+// Check that ./ isn't canonicalized away.
+// RUN: %clang_cl -internal-enable-pch -Werror /Yc./pchfile.h /FIpchfile.h /c -### -- %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-YC-I2 %s
+// CHECK-YC-I2: support for '/Yc' without a corresponding /FI flag not implemented yet; flag ignored
+
+// With an actual /I argument.
+// RUN: %clang_cl -internal-enable-pch -Werror /Ifoo /Ycpchfile.h /FIpchfile.h /c -### -- %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-YC-I3 %s
+// 1. This writes pchfile.pch into the root dir, even if this will pick up
+//    foo/pchfile.h
+// CHECK-YC-I3: cc1
+// CHECK-YC-I3: -emit-pch
+// CHECK-YC-I3: -o
+// CHECK-YC-I3: pchfile.pch
+// 2. Use .pch file.
+// CHECK-YC-I3: cc1
+// CHECK-YC-I3: -emit-obj
+// CHECK-YC-I3: -include-pch
+// CHECK-YC-I3: pchfile.pch
+
+// Check that ./ isn't canonicalized away for /Yu either.
+// RUN: %clang_cl -internal-enable-pch -Werror /Yupchfile.h /FI./pchfile.h /c -### -- %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-YU-I1 %s
+// CHECK-YU-I1: support for '/Yu' without a corresponding /FI flag not implemented yet; flag ignored
+
+// But /FIfoo/bar.h /Ycfoo\bar.h does work, as does /FIfOo.h /Ycfoo.H
+// FIXME: This part isn't implemented yet. The following two tests should not
+// show an error but do regular /Yu handling.
+// RUN: %clang_cl -internal-enable-pch -Werror /YupchFILE.h /FI./pchfile.h /c -### -- %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-YU-CASE %s
+// CHECK-YU-CASE: support for '/Yu' without a corresponding /FI flag not implemented yet; flag ignored
+// RUN: %clang_cl -internal-enable-pch -Werror /Yu./pchfile.h /FI.\pchfile.h /c -### -- %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-YU-SLASH %s
+// CHECK-YU-SLASH: support for '/Yu' without a corresponding /FI flag not implemented yet; flag ignored
+
+// cl.exe warns on multiple /Yc, /Yu, /Fp arguments, but clang-cl silently just
+// uses the last one.  This is true for e.g. /Fo too, so not warning on this
+// is self-consistent with clang-cl's flag handling.
+
+// Interaction with /fallback
+
+// /Yc /fallback => /Yc not passed on (but /FI is)
+// RUN: %clang_cl -internal-enable-pch -Werror /Ycpchfile.h /FIpchfile.h /Fpfoo.pch /fallback /c -### -- %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-YC-FALLBACK %s
+// Note that in /fallback builds, if creation of the pch fails the main compile
+// does still run so that /fallback can have an effect (this part is not tested)
+// CHECK-YC-FALLBACK: cc1
+// CHECK-YC-FALLBACK: -emit-obj
+// CHECK-YC-FALLBACK: -include-pch
+// CHECK-YC-FALLBACK: foo.pch
+// CHECK-YC-FALLBACK: ||
+// CHECK-YC-FALLBACK: cl.exe
+// CHECK-YC-FALLBACK-NOT: -include-pch
+// CHECK-YC-FALLBACK-NOT: /Ycpchfile.h
+// CHECK-YC-FALLBACK: /FIpchfile.h
+// CHECK-YC-FALLBACK-NOT: /Fpfoo.pch
+
+// /Yu /fallback => /Yu not passed on (but /FI is)
+// RUN: %clang_cl -internal-enable-pch -Werror /Yupchfile.h /FIpchfile.h /Fpfoo.pch /fallback /c -### -- %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-YU-FALLBACK %s
+// CHECK-YU-FALLBACK-NOT: -emit-pch
+// CHECK-YU-FALLBACK: cc1
+// CHECK-YU-FALLBACK: -emit-obj
+// CHECK-YU-FALLBACK: -include-pch
+// CHECK-YU-FALLBACK: foo.pch
+// CHECK-YU-FALLBACK: ||
+// CHECK-YU-FALLBACK: cl.exe
+// CHECK-YU-FALLBACK-NOT: -include-pch
+// CHECK-YU-FALLBACK-NOT: /Yupchfile.h
+// CHECK-YU-FALLBACK: /FIpchfile.h
+// CHECK-YU-FALLBACK-NOT: /Fpfoo.pch
+
+// /FI without /Yu => pch file not used, even if it exists (different from
+// -include, which picks up .gch files if they exist).
+// RUN: touch %t.pch
+// RUN: %clang_cl -internal-enable-pch -Werror /FI%t.pch /Fp%t.pch /c -### -- %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-FI %s
+// CHECK-FI-NOT: -include-pch
+// CHECK-FI: -include
+
+// Test interaction of /Yc with language mode flags.
+
+// If /TC changes the input language to C, a c pch file should be produced.
+// RUN: %clang_cl /TC -internal-enable-pch -Werror /Ycpchfile.h /FIpchfile.h /c -### -- %s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-YCTC %s
+// CHECK-YCTC: cc1
+// CHECK-YCTC: -emit-pch
+// CHECK-YCTC: -o
+// CHECK-YCTC: pchfile.pch
+// CHECK-YCTC: -x
+// CHECK-YCTP: "c"
+
+// Also check lower-case /Tc variant.
+// RUN: %clang_cl -internal-enable-pch -Werror /Ycpchfile.h /FIpchfile.h /c -### /Tc%s 2>&1 \
+// RUN:   | FileCheck -check-prefix=CHECK-YCTc %s
+// CHECK-YCTc: cc1
+// CHECK-YCTc: -emit-pch
+// CHECK-YCTc: -o
+// CHECK-YCTc: pchfile.pch
+// CHECK-YCTc: -x
+// CHECK-YCTc: "c"