clang-cl: Implement initial limited support for precompiled headers.

[thakis]

Summary

In the gcc precompiled header model, one explicitly runs clang with -x c++-header on a .h file to produce a gch file, and then includes the header with -include foo.h and if a .gch file exists for that header it gets used. This is documented at http://clang.llvm.org/docs/UsersManual.html#precompiled-headers

cl.exe's model is fairly different, and controlled by the two flags /Yc and /Yu. A pch file is generated as a side effect of a regular compilation when /Ycheader.h is passed. While the compilation is running, the compiler keeps track of #include lines in the main translation unit and writes everything up to an #include "header.h" line into a pch file. Conversely, /Yuheader.h tells the compiler to skip all code in the main TU up to and including #include "header.h" and instead load header.pch. (It's also possible to use /Yc and /Yu without an argument, in that case a #pragma hrdstop takes the role of controlling the point where pch ends and real code begins.)

This patch implements limited support for this in that it requires the pch header to be passed as a /FI force include flag – with this restriction, support for this can be implemented almost completely in the driver with fairly small amounts of code. For /Yu, this is trivial, and for /Yc a separate pch action is added that runs before the actual compilation. After r261774, the first failing command makes a compilation stop – this means if the pch fails to build, the main compilation won't run, which is what we want. However, in /fallback builds we need to run the main compilation even if the pch build fails, so that the main compilation's fallback can run. To achieve this, add a ForceSuccessCommand that pretends that the pch build always succeeded in /fallback builds (the main compilation will then fail to open the pch and run the fallback cl.exe invocation).

If /Yc /Yu are used in a setup that clang-cl doesn't implement yet, clang-cl will now emit a "not implemented yet, ignoring flag" warning that can be disabled by -Wno-clang-cl-pch.

Since clang-cl doesn't yet serialize some important things (most notably pragma comment(lib, ...), this feature is disabled by default and only enabled by an internal driver flag. Once it's more stable, this internal flag will disappear.

(The default stdafx.h setup passes stdafx.h as explicit argument to /Yc but not as /FI – instead every single TU has to #include <stdafx.h> as first thing it does. Implementing support for this should be possible with the approach in this patch with minimal frontend changes by passing a --stop-at / --start-at flag from the driver to the frontend. This is left for a follow-up. I don't think we ever want to support #pragma hdrstop, and supporting it with this approach isn't easy: This approach relies on the driver knowing the pch filename in advance, and #pragma hdrstop(out.pch) can set the output filename, so the driver can't know about it in advance.)

clang-cl now also honors /Fp and puts pch files in the same spot that cl.exe would put them, but the pch file format is of course incompatible. This has ramifications on /fallback, so /Yc /Yu aren't passed through to cl.exe in /fallback builds.

[thakis]

clean up accidentally duplicate if block

[hans]

Very nice!

I only have some style nits, really. Look forward to using this :-)

include/clang/Basic/DiagnosticDriverKinds.td

112

nit: I think it's more common in Clang's warnings to say "ignored" than "ignoring", and "flag ignored" saves one character :-)

Also I would have gone for a semicolon instead of comma, but this is not important.

Maybe "input" is redundant in "more than one input source file"?

</wordsmithing>

include/clang/Driver/CLCompatOptions.td

258

Can you add HelpText for these? I've tried to be good about documenting supported cl-mode flags.

lib/Driver/Driver.cpp

1448

A bit surprised that getValue() doesn't return a StringRef. But given that it doesn't, I suppose this is the nicest way to write it.

1466

FoundMatchingInclude?

2178

maybe add curlies around this else statement to make it a little easier to parse the else if that comes after?

2355

Maybe add .pch if needed?

lib/Driver/Tools.cpp

395

"the skip" -> just "skip"?

431

I got confused here, because even if we don't "continue", we still won't hit the else if (A->getOption().matches(options::OPT_include)) branch below.

But that branch is just dealing with implicit includes, we will still do the "Not translated, render as usual." step.

Maybe add a comment to the "else if" branch below that that code is for non-CL style PCH includes?

[thakis]

• rebase across jlebar's r261774 => implicit_inputs gone, ForceSuccessCommand is new
• .h file is found relative to include paths => introduce -find-pch-source= cc1 flag to handle that
• turns out several important things (#pragma comment(lib...)) aren't serialized yet => put this behind -internal-enable-pch for now so we can improve on this feature in-tree (and once it's ready that flag will go away again)
• address view comments

lib/Driver/Driver.cpp

2355

It already does this in the next line (?)

lib/Driver/Tools.cpp

431

Done I think, but I'm not sure I understood correctly what you were asking for.

[thakis]

forgot to svn add two new test files

[hans]

lgtm2

include/clang/Driver/Job.h

142 ↗

(On Diff #49544)

The second sentence looks weird.

lib/Driver/Driver.cpp

2355

Not a big deal, I just meant the comment would make it more obvious that it's about adding a pch *extension* to the filename if it says ".pch" instead of "pch". I know it becomes obvious later, but then my brain had already asked "what do you mean 'add pch'"?

lib/Driver/Tools.cpp

431

You got it.

lib/Frontend/CompilerInstance.cpp

746 ↗

(On Diff #49544)

Maybe add a comment about this FindPchSource mode

[thakis]

r262420, thanks!

include/clang/Basic/DiagnosticDriverKinds.td

def err_target_unsupported_arch
   : Error<"the target architecture '%0' is not supported by the target '%1'">;
 
 def err_drv_I_dash_not_supported : Error<
   "'%0' not supported, please use -iquote instead">;
 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, ignoring flag">,
+  InGroup<ClangClPch>;
+def warn_drv_ycyu_different_arg_clang_cl : Warning<
+  "support for '/Yc' and '/Yu' with different filenames not implemented yet, ignoring flags">,
+  InGroup<ClangClPch>;
+def warn_drv_ycyu_no_fi_arg_clang_cl : Warning<
+  "support for '%0' without a corresponding /FI flag not implemented yet, ignoring flag">,
+  InGroup<ClangClPch>;
+def warn_drv_yc_multiple_inputs_clang_cl : Warning<
+  "support for '/Yc' with more than one input source file not implemented yet, ignoring flag">,
+  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<
     "invalid option '%0' not of the form <from-file>;<to-file>">;
 def err_drv_invalid_gcc_output_type : Error<
     "invalid output type '%0' for use with gcc tool">;
 def err_drv_cc_print_options_failure : Error<
     "unable to open CC_PRINT_OPTIONS file: %0">;

include/clang/Basic/DiagnosticGroups.td

def Microsoft : DiagGroup<"microsoft",
      MicrosoftUsingDecl, MicrosoftMutableReference, MicrosoftPureDefinition,
      MicrosoftUnionMemberReference, MicrosoftExplicitConstructorCall,
      MicrosoftEnumValue, MicrosoftDefaultArgRedefinition, MicrosoftTemplate,
      MicrosoftRedeclareStatic, MicrosoftEnumForwardReference, MicrosoftGoto,
      MicrosoftFlexibleArray, MicrosoftExtraQualification, MicrosoftCast,
      MicrosoftConstInit, MicrosoftVoidPseudoDtor, MicrosoftAnonTag,
      MicrosoftCommentPaste, MicrosoftEndOfFile]>;
 
+def ClangClPch : DiagGroup<"clang-cl-pch">;
+
 def ObjCNonUnifiedException : DiagGroup<"objc-nonunified-exceptions">;
 
 def ObjCProtocolMethodImpl : DiagGroup<"objc-protocol-method-implementation">;
 
 def ObjCNoPropertyAutoSynthesis : DiagGroup<"objc-property-synthesis">;
 
 // ObjC API warning groups.
 def ObjCRedundantLiteralUse : DiagGroup<"objc-redundant-literal-use">;

include/clang/Driver/Action.h

 private:
   ActionClass Kind;
 
   /// The output type of this action.
   types::ID Type;
 
   ActionList Inputs;
 
+  /// Inputs that this Action depends on, but that aren't explicitly passed
+  /// as arguments to the action.
+  ///
+  /// For example, `clang-cl /Yc /Fifoo.h foo.cc` will first compile foo.h into
+  /// a pch file, and then load the pch file when compiling foo.cc.  If building
+  /// the pch file fails, foo.cc should not be compiled, so the action building
+  /// the pch file is an implicit input of the compile action.
+  ActionList ImplicitInputs;
+
 protected:
   Action(ActionClass Kind, types::ID Type) : Action(Kind, ActionList(), Type) {}
   Action(ActionClass Kind, Action *Input, types::ID Type)
       : Action(Kind, ActionList({Input}), Type) {}
+  Action(ActionClass Kind, Action *Input, const ActionList &ImplicitInputs,
+         types::ID Type)
+      : Kind(Kind), Type(Type), Inputs({Input}),
+        ImplicitInputs(ImplicitInputs) {}
   Action(ActionClass Kind, Action *Input)
       : Action(Kind, ActionList({Input}), Input->getType()) {}
   Action(ActionClass Kind, const ActionList &Inputs, types::ID Type)
       : Kind(Kind), Type(Type), Inputs(Inputs) {}
 
 public:
   virtual ~Action();
 
public:
   input_iterator input_begin() { return Inputs.begin(); }
   input_iterator input_end() { return Inputs.end(); }
   input_range inputs() { return input_range(input_begin(), input_end()); }
   input_const_iterator input_begin() const { return Inputs.begin(); }
   input_const_iterator input_end() const { return Inputs.end(); }
   input_const_range inputs() const {
     return input_const_range(input_begin(), input_end());
   }
+
+  input_const_iterator implicit_input_begin() const {
+    return ImplicitInputs.begin();
+  }
+  input_const_iterator implicit_input_end() const {
+    return ImplicitInputs.end();
+  }
+  input_const_range implicit_inputs() const {
+    return input_const_range(implicit_input_begin(), implicit_input_end());
+  }
 };
 
 class InputAction : public Action {
   virtual void anchor();
   const llvm::opt::Arg &Input;
 
 public:
   InputAction(const llvm::opt::Arg &Input, types::ID Type);
public:
 
   static bool classof(const Action *A) { return A->getKind() == CudaHostClass; }
 };
 
 class JobAction : public Action {
   virtual void anchor();
 protected:
   JobAction(ActionClass Kind, Action *Input, types::ID Type);
+  JobAction(ActionClass Kind, Action *Input, const ActionList &ImplicitInputs,
+            types::ID Type);
   JobAction(ActionClass Kind, const ActionList &Inputs, types::ID Type);
 
 public:
   static bool classof(const Action *A) {
     return (A->getKind() >= JobClassFirst &&
             A->getKind() <= JobClassLast);
   }
 };
public:
   static bool classof(const Action *A) {
     return A->getKind() == MigrateJobClass;
   }
 };
 
 class CompileJobAction : public JobAction {
   void anchor() override;
 public:
-  CompileJobAction(Action *Input, types::ID OutputType);
+  CompileJobAction(Action *Input, const ActionList &ImplicitInputs,
+                   types::ID OutputType);
 
   static bool classof(const Action *A) {
     return A->getKind() == CompileJobClass;
   }
 };
 
 class BackendJobAction : public JobAction {
   void anchor() override;

include/clang/Driver/CLCompatOptions.td

def _SLASH_vmv : CLFlag<"vmv">,
   HelpText<"Set the default most-general representation to "
            "virtual inheritance">;
 def _SLASH_volatile_ms  : Option<["/", "-"], "volatile:ms", KIND_FLAG>,
   Group<_SLASH_volatile_Group>, Flags<[CLOption, DriverOption]>,
   HelpText<"Volatile loads and stores have acquire and release semantics">;
 def _SLASH_Zl : CLFlag<"Zl">,
   HelpText<"Don't mention any default libraries in the object file">;
 
+def _SLASH_Yc : CLJoined<"Yc">;
+def _SLASH_Y_ : CLFlag<"Y-">;
+def _SLASH_Yu : CLJoined<"Yu">;
+def _SLASH_Fp : CLJoined<"Fp">;
+
 // Ignored:
 
 def _SLASH_analyze_ : CLIgnoredFlag<"analyze-">;
 def _SLASH_bigobj : CLIgnoredFlag<"bigobj">;
 def _SLASH_cgthreads : CLIgnoredJoined<"cgthreads">;
 def _SLASH_d2Zi_PLUS : CLIgnoredFlag<"d2Zi+">;
 def _SLASH_errorReport : CLIgnoredJoined<"errorReport">;
 def _SLASH_Fd : CLIgnoredJoined<"Fd">;

 def _SLASH_AI : CLJoined<"AI">;
 def _SLASH_clr : CLJoined<"clr">;
 def _SLASH_doc : CLJoined<"doc">;
 def _SLASH_FA_joined : CLJoined<"FA">;
 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">;
 def _SLASH_Fx : CLFlag<"Fx">;
 def _SLASH_G1 : CLFlag<"G1">;
 def _SLASH_G2 : CLFlag<"G2">;
 def _SLASH_Ge : CLFlag<"Ge">;
 def _SLASH_Gh : CLFlag<"Gh">;

 def _SLASH_Qimprecise_fwaits : CLFlag<"Qimprecise_fwaits">;
 def _SLASH_Qpar : CLFlag<"Qpar">;
 def _SLASH_Qvec_report : CLJoined<"Qvec-report">;
 def _SLASH_u : CLFlag<"u">;
 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">;
 def _SLASH_Zg : CLFlag<"Zg">;
 def _SLASH_ZI : CLFlag<"ZI">;
 def _SLASH_ZW : CLJoined<"ZW">;

include/clang/Driver/Driver.h

public:
   /// \return Whether any compilation should be built for this
   /// invocation.
   bool HandleImmediateArgs(const Compilation &C);
 
   /// ConstructAction - Construct the appropriate action to do for
   /// \p Phase on the \p Input, taking in to account arguments
   /// like -fsyntax-only or --analyze.
   Action *ConstructPhaseAction(Compilation &C, const llvm::opt::ArgList &Args,
-                               phases::ID Phase, Action *Input) const;
+                               phases::ID Phase, Action *Input,
+                               Action *ClangClPchInput = nullptr) const;
 
   /// BuildJobsForAction - Construct the jobs to perform for the action \p A and
   /// return an InputInfo for the result of running \p A.  Will only construct
   /// jobs for a given (Action, ToolChain, BoundArch) tuple once.
   InputInfo BuildJobsForAction(Compilation &C, const Action *A,
                                const ToolChain *TC, const char *BoundArch,
                                bool AtTopLevel, bool MultipleArchs,
                                const char *LinkingOutput,
const char *GetNamedOutputPath(Compilation &C,
                                  bool MultipleArchs) const;
 
   /// GetTemporaryPath - Return the pathname of a temporary file to use 
   /// as part of compilation; the file will have the given prefix and suffix.
   ///
   /// 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;
 
   /// Returns true if we are performing any kind of LTO.
   bool isUsingLTO() const { return LTOMode != LTOK_None; }
 
   /// Get the specific kind of LTO being performed.

lib/Driver/Action.cpp

 CudaHostAction::CudaHostAction(Action *Input, const ActionList &DeviceActions)
     : Action(CudaHostClass, Input), DeviceActions(DeviceActions) {}
 
 void JobAction::anchor() {}
 
 JobAction::JobAction(ActionClass Kind, Action *Input, types::ID Type)
     : Action(Kind, Input, Type) {}
 
+JobAction::JobAction(ActionClass Kind, Action *Input,
+                     const ActionList &ImplicitInputs, types::ID Type)
+    : Action(Kind, Input, ImplicitInputs, Type) {}
+
 JobAction::JobAction(ActionClass Kind, const ActionList &Inputs, types::ID Type)
   : Action(Kind, Inputs, Type) {
 }
 
 void PreprocessJobAction::anchor() {}
 
 PreprocessJobAction::PreprocessJobAction(Action *Input, types::ID OutputType)
     : JobAction(PreprocessJobClass, Input, OutputType) {}

 
 void MigrateJobAction::anchor() {}
 
 MigrateJobAction::MigrateJobAction(Action *Input, types::ID OutputType)
     : JobAction(MigrateJobClass, Input, OutputType) {}
 
 void CompileJobAction::anchor() {}
 
-CompileJobAction::CompileJobAction(Action *Input, types::ID OutputType)
-    : JobAction(CompileJobClass, Input, OutputType) {}
+CompileJobAction::CompileJobAction(Action *Input,
+                                   const ActionList &ImplicitInputs,
+                                   types::ID OutputType)
+    : JobAction(CompileJobClass, Input, ImplicitInputs, OutputType) {}
 
 void BackendJobAction::anchor() {}
 
 BackendJobAction::BackendJobAction(Action *Input, types::ID OutputType)
     : JobAction(BackendJobClass, Input, OutputType) {}
 
 void AssembleJobAction::anchor() {}
 

lib/Driver/Compilation.cpp

static bool ActionFailed(const Action *A,
   if (FailingCommands.empty())
     return false;
 
   for (FailingCommandList::const_iterator CI = FailingCommands.begin(),
          CE = FailingCommands.end(); CI != CE; ++CI)
     if (A == &(CI->second->getSource()))
       return true;
 
+  // Check if any of the actions that A depends on failed.
   for (const Action *AI : A->inputs())
     if (ActionFailed(AI, FailingCommands))
       return true;
+  for (const Action *AI : A->implicit_inputs())
+    if (ActionFailed(AI, FailingCommands))
+      return true;
 
   return false;
 }
 
 static bool InputsOk(const Command &C,
                      const FailingCommandList &FailingCommands) {
   return !ActionFailed(&C.getSource(), FailingCommands);
 }

lib/Driver/Driver.cpp

void Driver::BuildActions(Compilation &C, DerivedArgList &Args,
   if (Arg *A = Args.getLastArg(options::OPT__SLASH_o)) {
     if (A->getValue()[0] == '\0') {
       // It has to have a value.
       Diag(clang::diag::err_drv_missing_argument) << A->getSpelling() << 1;
       Args.eraseArg(options::OPT__SLASH_o);
     }
   }
 
+  // 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 Found = false;
+    for (const Arg *Inc : Args.filtered(options::OPT_include)) {
+      // FIXME: Do case-insensitive matching and consider / and \ as equal.
+      if (Inc->getValue() == Val)
+        Found = true;
+    }
+    if (!Found) {
+      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;
+  }
+
   // Construct the actions to perform.
   ActionList LinkerInputs;
 
   llvm::SmallVector<phases::ID, phases::MaxNumberOfPhases> PL;
   for (auto &I : Inputs) {
     types::ID InputType = I.first;
     const Arg *InputArg = I.second;
 
     PL.clear();
     types::getCompilationPhases(InputType, PL);
 
+    Action* ClangClPch = nullptr;
+    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 *InputArg = MakeInputArg(Args, Opts, YcArg->getValue());
+
+        // Build the pipeline for the pch file.
+        ClangClPch = C.MakeAction<InputAction>(*InputArg, InputType);
+        for (phases::ID Phase : PCHPL)
+          ClangClPch = ConstructPhaseAction(C, Args, Phase, ClangClPch);
+        assert(ClangClPch);
+        Actions.push_back(ClangClPch);
+      }
+    }
+
     // 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];
     if (InitialPhase > FinalPhase) {
       // Claim here to avoid the more general unused warning.
       InputArg->claim();
 
       // Suppress all unused style warnings with -Qunused-arguments
for (SmallVectorImpl<phases::ID>::iterator i = PL.begin(), e = PL.end();
 
       // Some types skip the assembler phase (e.g., llvm-bc), but we can't
       // encode this in the steps because the intermediate type depends on
       // arguments. Just special case here.
       if (Phase == phases::Assemble && Current->getType() != types::TY_PP_Asm)
         continue;
 
       // Otherwise construct the appropriate action.
+      if (Phase == phases::Compile)
+        Current = ConstructPhaseAction(C, Args, Phase, Current, ClangClPch);
+      else
         Current = ConstructPhaseAction(C, Args, Phase, Current);
 
       if (InputType == types::TY_CUDA && Phase == CudaInjectionPhase) {
         Current = buildCudaActions(C, Args, InputArg, Current, Actions);
         if (!Current)
           break;
       }
 
       if (Current->getType() == types::TY_Nothing)
void Driver::BuildActions(Compilation &C, DerivedArgList &Args,
   Args.ClaimAllArgs(options::OPT_cl_ignored_Group);
 
   // Claim --cuda-host-only arg which may be passed to non-CUDA
   // compilations and should not trigger warnings there.
   Args.ClaimAllArgs(options::OPT_cuda_host_only);
 }
 
 Action *Driver::ConstructPhaseAction(Compilation &C, const ArgList &Args,
-                                     phases::ID Phase, Action *Input) const {
+                                     phases::ID Phase, Action *Input,
+                                     Action *ClangClPchInput) const {
   llvm::PrettyStackTraceString CrashInfo("Constructing phase actions");
   // Build the appropriate action.
   switch (Phase) {
   case phases::Link:
     llvm_unreachable("link action invalid here.");
   case phases::Preprocess: {
     types::ID OutputTy;
     // -{M, MM} alter the output type.
case phases::Precompile: {
     types::ID OutputTy = types::TY_PCH;
     if (Args.hasArg(options::OPT_fsyntax_only)) {
       // Syntax checks should not emit a PCH file
       OutputTy = types::TY_Nothing;
     }
     return C.MakeAction<PrecompileJobAction>(Input, OutputTy);
   }
   case phases::Compile: {
+    ActionList ImplicitInputs;
+
+    // Don't make the pch action an implicit input in /fallback builds, so that
+    // if the pch compilation fails, the main compilation with the fallback
+    // still runs.
+    if (ClangClPchInput && !Args.hasArg(options::OPT__SLASH_fallback))
+      ImplicitInputs.push_back(ClangClPchInput);
+
     if (Args.hasArg(options::OPT_fsyntax_only))
-      return C.MakeAction<CompileJobAction>(Input, types::TY_Nothing);
+      return C.MakeAction<CompileJobAction>(Input, ImplicitInputs,
+                                            types::TY_Nothing);
     if (Args.hasArg(options::OPT_rewrite_objc))
-      return C.MakeAction<CompileJobAction>(Input, types::TY_RewrittenObjC);
+      return C.MakeAction<CompileJobAction>(Input, ImplicitInputs,
+                                            types::TY_RewrittenObjC);
     if (Args.hasArg(options::OPT_rewrite_legacy_objc))
-      return C.MakeAction<CompileJobAction>(Input,
+      return C.MakeAction<CompileJobAction>(Input, ImplicitInputs,
                                             types::TY_RewrittenLegacyObjC);
-    if (Args.hasArg(options::OPT__analyze, options::OPT__analyze_auto))
+    if (Args.hasArg(options::OPT__analyze, options::OPT__analyze_auto)) {
+      assert(!ClangClPchInput);
       return C.MakeAction<AnalyzeJobAction>(Input, types::TY_Plist);
-    if (Args.hasArg(options::OPT__migrate))
+    }
+    if (Args.hasArg(options::OPT__migrate)) {
+      assert(!ClangClPchInput);
       return C.MakeAction<MigrateJobAction>(Input, types::TY_Remap);
+    }
     if (Args.hasArg(options::OPT_emit_ast))
-      return C.MakeAction<CompileJobAction>(Input, types::TY_AST);
+      return C.MakeAction<CompileJobAction>(Input, ImplicitInputs,
+                                            types::TY_AST);
     if (Args.hasArg(options::OPT_module_file_info))
-      return C.MakeAction<CompileJobAction>(Input, types::TY_ModuleFile);
-    if (Args.hasArg(options::OPT_verify_pch))
+      return C.MakeAction<CompileJobAction>(Input, ImplicitInputs,
+                                            types::TY_ModuleFile);
+    if (Args.hasArg(options::OPT_verify_pch)) {
+      assert(!ClangClPchInput);
       return C.MakeAction<VerifyPCHJobAction>(Input, types::TY_Nothing);
-    return C.MakeAction<CompileJobAction>(Input, types::TY_LLVM_BC);
+    }
+    return C.MakeAction<CompileJobAction>(Input, ImplicitInputs,
+                                          types::TY_LLVM_BC);
   }
   case phases::Backend: {
     if (isUsingLTO()) {
       types::ID Output =
           Args.hasArg(options::OPT_S) ? types::TY_LTO_IR : types::TY_LTO_BC;
       return C.MakeAction<BackendJobAction>(Input, Output);
     }
     if (Args.hasArg(options::OPT_emit_llvm)) {
if (IsCLMode()) {
       // clang-cl uses BaseName for the executable name.
       NamedOutput =
           MakeCLOutputFilename(C.getArgs(), "", BaseName, types::TY_Image);
     } else if (MultipleArchs && BoundArch) {
       SmallString<128> Output(getDefaultImageName());
       Output += "-";
       Output.append(BoundArch);
       NamedOutput = C.getArgs().MakeArgString(Output.c_str());
     } 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.");
 
     std::string::size_type End = std::string::npos;
     if (!types::appendSuffixForType(JA.getType()))
       End = BaseName.rfind('.');
     SmallString<128> Suffixed(BaseName.substr(0, End));
std::string Driver::GetTemporaryPath(StringRef Prefix,
   if (EC) {
     Diag(clang::diag::err_unable_to_make_temp) << EC.message();
     return "";
   }
 
   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();
+
+    // Add pch if needed: "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 {
 
   ToolChain *&TC = ToolChains[Target.str()];
   if (!TC) {
     switch (Target.getOS()) {
     case llvm::Triple::CloudABI:
       TC = new toolchains::CloudABI(*this, Target, Args);

lib/Driver/Tools.cpp

for (const Arg *A : Args.filtered(options::OPT_MT, options::OPT_MQ)) {
     }
   }
 
   // Add -i* options, and automatically translate to
   // -include-pch/-include-pth for transparent PCH support. It's
   // 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 the 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;
+    }
+  }
+
   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)) {
       bool IsFirstImplicitInclude = !RenderedImplicitInclude;
       RenderedImplicitInclude = true;
 
       // Use PCH if the user requested it.
       bool UsePCH = D.CCCUsePCH;
 
       bool FoundPTH = false;
       bool FoundPCH = false;

test/Driver/Inputs/pchfile.h

+#if defined(ERR_HEADER)
+#error nope1
+#endif

test/Driver/cl-pch.c

+// 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 -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 -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 -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 -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++"

test/Driver/cl-pch.cpp

+// 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 -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 -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 -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 -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 -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 -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 -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, ignoring flags
+
+// Similarly, punt on /Yc with more than one input file.
+// RUN: %clang_cl -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 input source file not implemented yet, ignoring flag
+
+// /Yc /Yu /Y-
+// RUN: %clang_cl -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 -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 -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 -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 -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 -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 -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 -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 -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 -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, ignoring flag
+// RUN: %clang_cl -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, ignoring flag
+
+// /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 -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, ignoring flag
+
+// Check that ./ isn't canonicalized away.
+// RUN: %clang_cl -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, ignoring flag
+
+// With an actual /I argument.
+// RUN: %clang_cl -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 -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, ignoring flag
+
+// 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 -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, ignoring flag
+// RUN: %clang_cl -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, ignoring flag
+
+// 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 -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 -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 -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 -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 -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"