Update clang, llvm, lld, lldb, compiler-rt and libc++ to 4.0.0 release:

MFC r309142 (by emaste):

Add WITH_LLD_AS_LD build knob

If set it installs LLD as /usr/bin/ld.  LLD (as of version 3.9) is not
capable of linking the world and kernel, but can self-host and link many
substantial applications. GNU ld continues to be used for the world and
kernel build, regardless of how this knob is set.

It is on by default for arm64, and off for all other CPU architectures.

Sponsored by:	The FreeBSD Foundation

MFC r310840:

Reapply 310775, now it also builds correctly if lldb is disabled:

Move llvm-objdump from CLANG_EXTRAS to installed by default

We currently install three tools from binutils 2.17.50: as, ld, and
objdump. Work is underway to migrate to a permissively-licensed
tool-chain, with one goal being the retirement of binutils 2.17.50.

LLVM's llvm-objdump is intended to be compatible with GNU objdump
although it is currently missing some options and may have formatting
differences. Enable it by default for testing and further investigation.
It may later be changed to install as /usr/bin/objdump, it becomes a
fully viable replacement.

Reviewed by:	emaste
Differential Revision:	https://reviews.freebsd.org/D8879

MFC r312855 (by emaste):

Rename LLD_AS_LD to LLD_IS_LD, for consistency with CLANG_IS_CC

Reported by:	Dan McGregor <dan.mcgregor usask.ca>

MFC r313559 | glebius | 2017-02-10 18:34:48 +0100 (Fri, 10 Feb 2017) | 5 lines

Don't check struct rtentry on FreeBSD, it is an internal kernel structure.
On other systems it may be API structure for SIOCADDRT/SIOCDELRT.

Reviewed by:	emaste, dim

MFC r314152 (by jkim):

Remove an assembler flag, which is redundant since r309124.  The upstream
took care of it by introducing a macro NO_EXEC_STACK_DIRECTIVE.

http://llvm.org/viewvc/llvm-project?rev=273500&view=rev

Reviewed by:	dim

MFC r314564:

Upgrade our copies of clang, llvm, lld, lldb, compiler-rt and libc++ to
4.0.0 (branches/release_40 296509).  The release will follow soon.

Please note that from 3.5.0 onwards, clang, llvm and lldb require C++11
support to build; see UPDATING for more information.

Also note that as of 4.0.0, lld should be able to link the base system
on amd64 and aarch64.  See the WITH_LLD_IS_LLD setting in src.conf(5).
Though please be aware that this is work in progress.

Release notes for llvm, clang and lld will be available here:
<http://releases.llvm.org/4.0.0/docs/ReleaseNotes.html>
<http://releases.llvm.org/4.0.0/tools/clang/docs/ReleaseNotes.html>
<http://releases.llvm.org/4.0.0/tools/lld/docs/ReleaseNotes.html>

Thanks to Ed Maste, Jan Beich, Antoine Brodin and Eric Fiselier for
their help.

Relnotes:	yes
Exp-run:	antoine
PR:		215969, 216008

MFC r314708:

For now, revert r287232 from upstream llvm trunk (by Daniil Fukalov):

  [SCEV] limit recursion depth of CompareSCEVComplexity

  Summary:
  CompareSCEVComplexity goes too deep (50+ on a quite a big unrolled
  loop) and runs almost infinite time.

  Added cache of "equal" SCEV pairs to earlier cutoff of further
  estimation. Recursion depth limit was also introduced as a parameter.

  Reviewers: sanjoy

  Subscribers: mzolotukhin, tstellarAMD, llvm-commits

  Differential Revision: https://reviews.llvm.org/D26389

This commit is the cause of excessive compile times on skein_block.c
(and possibly other files) during kernel builds on amd64.

We never saw the problematic behavior described in this upstream commit,
so for now it is better to revert it.  An upstream bug has been filed
here: https://bugs.llvm.org/show_bug.cgi?id=32142

Reported by:	mjg

MFC r314795:

Reapply r287232 from upstream llvm trunk (by Daniil Fukalov):

  [SCEV] limit recursion depth of CompareSCEVComplexity

  Summary:
  CompareSCEVComplexity goes too deep (50+ on a quite a big unrolled
  loop) and runs almost infinite time.

  Added cache of "equal" SCEV pairs to earlier cutoff of further
  estimation. Recursion depth limit was also introduced as a parameter.

  Reviewers: sanjoy

  Subscribers: mzolotukhin, tstellarAMD, llvm-commits

  Differential Revision: https://reviews.llvm.org/D26389

Pull in r296992 from upstream llvm trunk (by Sanjoy Das):

  [SCEV] Decrease the recursion threshold for CompareValueComplexity

  Fixes PR32142.

  r287232 accidentally increased the recursion threshold for
  CompareValueComplexity from 2 to 32.  This change reverses that
  change by introducing a separate flag for CompareValueComplexity's
  threshold.

The latter revision fixes the excessive compile times for skein_block.c.

MFC r314907 | mmel | 2017-03-08 12:40:27 +0100 (Wed, 08 Mar 2017) | 7 lines

Unbreak ARMv6 world.

The new compiler_rt library imported with clang 4.0.0 have several fatal
issues (non-functional __udivsi3 for example) with ARM specific instrict
functions. As temporary workaround, until upstream solve these problems,
disable all thumb[1][2] related feature.

MFC r315016:

Update clang, llvm, lld, lldb, compiler-rt and libc++ to 4.0.0 release.
We were already very close to the last release candidate, so this is a
pretty minor update.

Relnotes:	yes

MFC r316005:

Revert r314907, and pull in r298713 from upstream compiler-rt trunk (by
Weiming Zhao):

  builtins: Select correct code fragments when compiling for Thumb1/Thum2/ARM ISA.

  Summary:
  Value of __ARM_ARCH_ISA_THUMB isn't based on the actual compilation
  mode (-mthumb, -marm), it reflect's capability of given CPU.

  Due to this:
   - use  __tbumb__ and __thumb2__ insteand of __ARM_ARCH_ISA_THUMB
   - use '.thumb' directive consistently  in all affected files
   - decorate all thumb functions using
     DEFINE_COMPILERRT_THUMB_FUNCTION()

  ---------
  Note: This patch doesn't fix broken Thumb1 variant of __udivsi3 !

  Reviewers: weimingz, rengolin, compnerd

  Subscribers: aemerson, dim

  Differential Revision: https://reviews.llvm.org/D30938

Discussed with:	mmel

1 files changed, 221 insertions, 45 deletions

diff --git a/contrib/llvm/tools/clang/lib/Frontend/CompilerInstance.cpp b/contrib/llvm/tools/clang/lib/Frontend/CompilerInstance.cpp
index 8b00a3d..afcaa6e 100644
--- a/contrib/llvm/tools/clang/lib/Frontend/CompilerInstance.cpp
+++ b/contrib/llvm/tools/clang/lib/Frontend/CompilerInstance.cpp
@@ -29,6 +29,7 @@
 #include "clang/Lex/HeaderSearch.h"
 #include "clang/Lex/PTHManager.h"
 #include "clang/Lex/Preprocessor.h"
+#include "clang/Lex/PreprocessorOptions.h"
 #include "clang/Sema/CodeCompleteConsumer.h"
 #include "clang/Sema/Sema.h"
 #include "clang/Serialization/ASTReader.h"
@@ -65,8 +66,9 @@ CompilerInstance::~CompilerInstance() {
   assert(OutputFiles.empty() && "Still output files in flight?");
 }
 
-void CompilerInstance::setInvocation(CompilerInvocation *Value) {
-  Invocation = Value;
+void CompilerInstance::setInvocation(
+    std::shared_ptr<CompilerInvocation> Value) {
+  Invocation = std::move(Value);
 }
 
 bool CompilerInstance::shouldBuildGlobalModuleIndex() const {
@@ -95,7 +97,9 @@ void CompilerInstance::setSourceManager(SourceManager *Value) {
   SourceMgr = Value;
 }
 
-void CompilerInstance::setPreprocessor(Preprocessor *Value) { PP = Value; }
+void CompilerInstance::setPreprocessor(std::shared_ptr<Preprocessor> Value) {
+  PP = std::move(Value);
+}
 
 void CompilerInstance::setASTContext(ASTContext *Value) {
   Context = Value;
@@ -140,6 +144,66 @@ void CompilerInstance::setModuleDepCollector(
   ModuleDepCollector = std::move(Collector);
 }
 
+static void collectHeaderMaps(const HeaderSearch &HS,
+                              std::shared_ptr<ModuleDependencyCollector> MDC) {
+  SmallVector<std::string, 4> HeaderMapFileNames;
+  HS.getHeaderMapFileNames(HeaderMapFileNames);
+  for (auto &Name : HeaderMapFileNames)
+    MDC->addFile(Name);
+}
+
+static void collectIncludePCH(CompilerInstance &CI,
+                              std::shared_ptr<ModuleDependencyCollector> MDC) {
+  const PreprocessorOptions &PPOpts = CI.getPreprocessorOpts();
+  if (PPOpts.ImplicitPCHInclude.empty())
+    return;
+
+  StringRef PCHInclude = PPOpts.ImplicitPCHInclude;
+  FileManager &FileMgr = CI.getFileManager();
+  const DirectoryEntry *PCHDir = FileMgr.getDirectory(PCHInclude);
+  if (!PCHDir) {
+    MDC->addFile(PCHInclude);
+    return;
+  }
+
+  std::error_code EC;
+  SmallString<128> DirNative;
+  llvm::sys::path::native(PCHDir->getName(), DirNative);
+  vfs::FileSystem &FS = *FileMgr.getVirtualFileSystem();
+  SimpleASTReaderListener Validator(CI.getPreprocessor());
+  for (vfs::directory_iterator Dir = FS.dir_begin(DirNative, EC), DirEnd;
+       Dir != DirEnd && !EC; Dir.increment(EC)) {
+    // Check whether this is an AST file. ASTReader::isAcceptableASTFile is not
+    // used here since we're not interested in validating the PCH at this time,
+    // but only to check whether this is a file containing an AST.
+    if (!ASTReader::readASTFileControlBlock(
+            Dir->getName(), FileMgr, CI.getPCHContainerReader(),
+            /*FindModuleFileExtensions=*/false, Validator,
+            /*ValidateDiagnosticOptions=*/false))
+      MDC->addFile(Dir->getName());
+  }
+}
+
+static void collectVFSEntries(CompilerInstance &CI,
+                              std::shared_ptr<ModuleDependencyCollector> MDC) {
+  if (CI.getHeaderSearchOpts().VFSOverlayFiles.empty())
+    return;
+
+  // Collect all VFS found.
+  SmallVector<vfs::YAMLVFSEntry, 16> VFSEntries;
+  for (const std::string &VFSFile : CI.getHeaderSearchOpts().VFSOverlayFiles) {
+    llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> Buffer =
+        llvm::MemoryBuffer::getFile(VFSFile);
+    if (!Buffer)
+      return;
+    vfs::collectVFSFromYAML(std::move(Buffer.get()), /*DiagHandler*/ nullptr,
+                            VFSFile, VFSEntries);
+  }
+
+  for (auto &E : VFSEntries)
+    MDC->addFile(E.VPath, E.RPath);
+}
+
 // Diagnostics
 static void SetUpDiagnosticLog(DiagnosticOptions *DiagOpts,
                                const CodeGenOptions *CodeGenOpts,
@@ -304,14 +368,13 @@ void CompilerInstance::createPreprocessor(TranslationUnitKind TUKind) {
     PTHMgr = PTHManager::Create(PPOpts.TokenCache, getDiagnostics());
 
   // Create the Preprocessor.
-  HeaderSearch *HeaderInfo = new HeaderSearch(&getHeaderSearchOpts(),
-                                              getSourceManager(),
-                                              getDiagnostics(),
-                                              getLangOpts(),
-                                              &getTarget());
-  PP = new Preprocessor(&getPreprocessorOpts(), getDiagnostics(), getLangOpts(),
-                        getSourceManager(), *HeaderInfo, *this, PTHMgr,
-                        /*OwnsHeaderSearch=*/true, TUKind);
+  HeaderSearch *HeaderInfo =
+      new HeaderSearch(getHeaderSearchOptsPtr(), getSourceManager(),
+                       getDiagnostics(), getLangOpts(), &getTarget());
+  PP = std::make_shared<Preprocessor>(
+      Invocation->getPreprocessorOptsPtr(), getDiagnostics(), getLangOpts(),
+      getSourceManager(), *HeaderInfo, *this, PTHMgr,
+      /*OwnsHeaderSearch=*/true, TUKind);
   PP->Initialize(getTarget(), getAuxTarget());
 
   // Note that this is different then passing PTHMgr to Preprocessor's ctor.
@@ -333,9 +396,16 @@ void CompilerInstance::createPreprocessor(TranslationUnitKind TUKind) {
   InitializePreprocessor(*PP, PPOpts, getPCHContainerReader(),
                          getFrontendOpts());
 
-  // Initialize the header search object.
+  // Initialize the header search object.  In CUDA compilations, we use the aux
+  // triple (the host triple) to initialize our header search, since we need to
+  // find the host headers in order to compile the CUDA code.
+  const llvm::Triple *HeaderSearchTriple = &PP->getTargetInfo().getTriple();
+  if (PP->getTargetInfo().getTriple().getOS() == llvm::Triple::CUDA &&
+      PP->getAuxTargetInfo())
+    HeaderSearchTriple = &PP->getAuxTargetInfo()->getTriple();
+
   ApplyHeaderSearchOptions(PP->getHeaderSearchInfo(), getHeaderSearchOpts(),
-                           PP->getLangOpts(), PP->getTargetInfo().getTriple());
+                           PP->getLangOpts(), *HeaderSearchTriple);
 
   PP->setPreprocessedOutput(getPreprocessorOutputOpts().ShowCPP);
 
@@ -358,8 +428,14 @@ void CompilerInstance::createPreprocessor(TranslationUnitKind TUKind) {
         DepOpts.ModuleDependencyOutputDir);
   }
 
-  if (ModuleDepCollector)
+  // If there is a module dep collector, register with other dep collectors
+  // and also (a) collect header maps and (b) TODO: input vfs overlay files.
+  if (ModuleDepCollector) {
     addDependencyCollector(ModuleDepCollector);
+    collectHeaderMaps(PP->getHeaderSearchInfo(), ModuleDepCollector);
+    collectIncludePCH(*this, ModuleDepCollector);
+    collectVFSEntries(*this, ModuleDepCollector);
+  }
 
   for (auto &Listener : DependencyCollectors)
     Listener->attachToPreprocessor(*PP);
@@ -424,7 +500,7 @@ IntrusiveRefCntPtr<ASTReader> CompilerInstance::createPCHExternalASTSource(
     StringRef Path, StringRef Sysroot, bool DisablePCHValidation,
     bool AllowPCHWithCompilerErrors, Preprocessor &PP, ASTContext &Context,
     const PCHContainerReader &PCHContainerRdr,
-    ArrayRef<IntrusiveRefCntPtr<ModuleFileExtension>> Extensions,
+    ArrayRef<std::shared_ptr<ModuleFileExtension>> Extensions,
     void *DeserializationListener, bool OwnDeserializationListener,
     bool Preamble, bool UseGlobalModuleIndex) {
   HeaderSearchOptions &HSOpts = PP.getHeaderSearchInfo().getHeaderSearchOpts();
@@ -514,9 +590,11 @@ void CompilerInstance::createCodeCompletionConsumer() {
 }
 
 void CompilerInstance::createFrontendTimer() {
-  FrontendTimerGroup.reset(new llvm::TimerGroup("Clang front-end time report"));
+  FrontendTimerGroup.reset(
+      new llvm::TimerGroup("frontend", "Clang front-end time report"));
   FrontendTimer.reset(
-      new llvm::Timer("Clang front-end timer", *FrontendTimerGroup));
+      new llvm::Timer("frontend", "Clang front-end timer",
+                      *FrontendTimerGroup));
 }
 
 CodeCompleteConsumer *
@@ -537,6 +615,11 @@ void CompilerInstance::createSema(TranslationUnitKind TUKind,
                                   CodeCompleteConsumer *CompletionConsumer) {
   TheSema.reset(new Sema(getPreprocessor(), getASTContext(), getASTConsumer(),
                          TUKind, CompletionConsumer));
+  // Attach the external sema source if there is any.
+  if (ExternalSemaSrc) {
+    TheSema->addExternalSource(ExternalSemaSrc.get());
+    ExternalSemaSrc->InitializeSema(*TheSema);
+  }
 }
 
 // Output Files
@@ -841,6 +924,9 @@ bool CompilerInstance::ExecuteAction(FrontendAction &Act) {
   // created. This complexity should be lifted elsewhere.
   getTarget().adjust(getLangOpts());
 
+  // Adjust target options based on codegen options.
+  getTarget().adjustTargetOptions(getCodeGenOpts(), getTargetOpts());
+
   // rewriter project will change target built-in bool type from its default. 
   if (getFrontendOpts().ProgramAction == frontend::RewriteObjC)
     getTarget().noSignedCharForObjCBool();
@@ -854,8 +940,8 @@ bool CompilerInstance::ExecuteAction(FrontendAction &Act) {
   if (getFrontendOpts().ShowTimers)
     createFrontendTimer();
 
-  if (getFrontendOpts().ShowStats)
-    llvm::EnableStatistics();
+  if (getFrontendOpts().ShowStats || !getFrontendOpts().StatsFile.empty())
+    llvm::EnableStatistics(false);
 
   for (const FrontendInputFile &FIF : getFrontendOpts().Inputs) {
     // Reset the ID tables if we are reusing the SourceManager and parsing
@@ -888,9 +974,24 @@ bool CompilerInstance::ExecuteAction(FrontendAction &Act) {
       OS << " generated.\n";
   }
 
-  if (getFrontendOpts().ShowStats && hasFileManager()) {
-    getFileManager().PrintStats();
-    OS << "\n";
+  if (getFrontendOpts().ShowStats) {
+    if (hasFileManager()) {
+      getFileManager().PrintStats();
+      OS << '\n';
+    }
+    llvm::PrintStatistics(OS);
+  }
+  StringRef StatsFile = getFrontendOpts().StatsFile;
+  if (!StatsFile.empty()) {
+    std::error_code EC;
+    auto StatS = llvm::make_unique<llvm::raw_fd_ostream>(StatsFile, EC,
+                                                         llvm::sys::fs::F_Text);
+    if (EC) {
+      getDiagnostics().Report(diag::warn_fe_unable_to_open_stats_file)
+          << StatsFile << EC.message();
+    } else {
+      llvm::PrintStatisticsJSON(*StatS);
+    }
   }
 
   return !getDiagnostics().getClient()->getNumErrors();
@@ -919,8 +1020,8 @@ static bool compileModuleImpl(CompilerInstance &ImportingInstance,
     = ImportingInstance.getPreprocessor().getHeaderSearchInfo().getModuleMap();
     
   // Construct a compiler invocation for creating this module.
-  IntrusiveRefCntPtr<CompilerInvocation> Invocation
-    (new CompilerInvocation(ImportingInstance.getInvocation()));
+  auto Invocation =
+      std::make_shared<CompilerInvocation>(ImportingInstance.getInvocation());
 
   PreprocessorOptions &PPOpts = Invocation->getPreprocessorOpts();
   
@@ -936,7 +1037,8 @@ static bool compileModuleImpl(CompilerInstance &ImportingInstance,
       std::remove_if(PPOpts.Macros.begin(), PPOpts.Macros.end(),
                      [&HSOpts](const std::pair<std::string, bool> &def) {
         StringRef MacroDef = def.first;
-        return HSOpts.ModulesIgnoreMacros.count(MacroDef.split('=').first) > 0;
+        return HSOpts.ModulesIgnoreMacros.count(
+                   llvm::CachedHashString(MacroDef.split('=').first)) > 0;
       }),
       PPOpts.Macros.end());
 
@@ -949,7 +1051,8 @@ static bool compileModuleImpl(CompilerInstance &ImportingInstance,
   PreprocessorOptions &ImportingPPOpts
     = ImportingInstance.getInvocation().getPreprocessorOpts();
   if (!ImportingPPOpts.FailedModules)
-    ImportingPPOpts.FailedModules = new PreprocessorOptions::FailedModulesSet;
+    ImportingPPOpts.FailedModules =
+        std::make_shared<PreprocessorOptions::FailedModulesSet>();
   PPOpts.FailedModules = ImportingPPOpts.FailedModules;
 
   // If there is a module map file, build the module using the module map.
@@ -974,7 +1077,8 @@ static bool compileModuleImpl(CompilerInstance &ImportingInstance,
   // module.
   CompilerInstance Instance(ImportingInstance.getPCHContainerOperations(),
                             /*BuildingModule=*/true);
-  Instance.setInvocation(&*Invocation);
+  auto &Inv = *Invocation;
+  Instance.setInvocation(std::move(Invocation));
 
   Instance.createDiagnostics(new ForwardingDiagnosticConsumer(
                                    ImportingInstance.getDiagnosticClient()),
@@ -996,7 +1100,7 @@ static bool compileModuleImpl(CompilerInstance &ImportingInstance,
   // between all of the module CompilerInstances. Other than that, we don't
   // want to produce any dependency output from the module build.
   Instance.setModuleDepCollector(ImportingInstance.getModuleDepCollector());
-  Invocation->getDependencyOutputOpts() = DependencyOutputOptions();
+  Inv.getDependencyOutputOpts() = DependencyOutputOptions();
 
   // Get or create the module map that we'll use to build this module.
   std::string InferredModuleMapContent;
@@ -1022,7 +1126,7 @@ static bool compileModuleImpl(CompilerInstance &ImportingInstance,
 
   // Construct a module-generating action. Passing through the module map is
   // safe because the FileManager is shared between the compiler instances.
-  GenerateModuleAction CreateModuleAction(
+  GenerateModuleFromModuleMapAction CreateModuleAction(
       ModMap.getModuleMapFileForUniquing(Module), Module->IsSystem);
 
   ImportingInstance.getDiagnostics().Report(ImportLoc,
@@ -1292,7 +1396,8 @@ void CompilerInstance::createModuleManager() {
     const PreprocessorOptions &PPOpts = getPreprocessorOpts();
     std::unique_ptr<llvm::Timer> ReadTimer;
     if (FrontendTimerGroup)
-      ReadTimer = llvm::make_unique<llvm::Timer>("Reading modules",
+      ReadTimer = llvm::make_unique<llvm::Timer>("reading_modules",
+                                                 "Reading modules",
                                                  *FrontendTimerGroup);
     ModuleManager = new ASTReader(
         getPreprocessor(), getASTContext(), getPCHContainerReader(),
@@ -1325,7 +1430,8 @@ void CompilerInstance::createModuleManager() {
 bool CompilerInstance::loadModuleFile(StringRef FileName) {
   llvm::Timer Timer;
   if (FrontendTimerGroup)
-    Timer.init("Preloading " + FileName.str(), *FrontendTimerGroup);
+    Timer.init("preloading." + FileName.str(), "Preloading " + FileName.str(),
+               *FrontendTimerGroup);
   llvm::TimeRegion TimeLoading(FrontendTimerGroup ? &Timer : nullptr);
 
   // Helper to recursively read the module names for all modules we're adding.
@@ -1357,8 +1463,21 @@ bool CompilerInstance::loadModuleFile(StringRef FileName) {
         if (Module *M = CI.getPreprocessor()
                             .getHeaderSearchInfo()
                             .getModuleMap()
-                            .findModule(II->getName()))
+                            .findModule(II->getName())) {
           M->HasIncompatibleModuleFile = true;
+
+          // Mark module as available if the only reason it was unavailable
+          // was missing headers.
+          SmallVector<Module *, 2> Stack;
+          Stack.push_back(M);
+          while (!Stack.empty()) {
+            Module *Current = Stack.pop_back_val();
+            if (Current->IsMissingRequirement) continue;
+            Current->IsAvailable = true;
+            Stack.insert(Stack.end(),
+                         Current->submodule_begin(), Current->submodule_end());
+          }
+        }
       }
       LoadedModules.clear();
     }
@@ -1432,7 +1551,25 @@ CompilerInstance::loadModule(SourceLocation ImportLoc,
   } else {
     // Search for a module with the given name.
     Module = PP->getHeaderSearchInfo().lookupModule(ModuleName);
-    if (!Module) {
+    HeaderSearchOptions &HSOpts =
+        PP->getHeaderSearchInfo().getHeaderSearchOpts();
+
+    std::string ModuleFileName;
+    bool LoadFromPrebuiltModulePath = false;
+    // We try to load the module from the prebuilt module paths. If not
+    // successful, we then try to find it in the module cache.
+    if (!HSOpts.PrebuiltModulePaths.empty()) {
+      // Load the module from the prebuilt module path.
+      ModuleFileName = PP->getHeaderSearchInfo().getModuleFileName(
+          ModuleName, "", /*UsePrebuiltPath*/ true);
+      if (!ModuleFileName.empty())
+        LoadFromPrebuiltModulePath = true;
+    }
+    if (!LoadFromPrebuiltModulePath && Module) {
+      // Load the module from the module cache.
+      ModuleFileName = PP->getHeaderSearchInfo().getModuleFileName(Module);
+    } else if (!LoadFromPrebuiltModulePath) {
+      // We can't find a module, error out here.
       getDiagnostics().Report(ModuleNameLoc, diag::err_module_not_found)
       << ModuleName
       << SourceRange(ImportLoc, ModuleNameLoc);
@@ -1440,13 +1577,11 @@ CompilerInstance::loadModule(SourceLocation ImportLoc,
       return ModuleLoadResult();
     }
 
-    std::string ModuleFileName =
-        PP->getHeaderSearchInfo().getModuleFileName(Module);
     if (ModuleFileName.empty()) {
-      if (Module->HasIncompatibleModuleFile) {
+      if (Module && Module->HasIncompatibleModuleFile) {
         // We tried and failed to load a module file for this module. Fall
         // back to textual inclusion for its headers.
-        return ModuleLoadResult(nullptr, /*missingExpected*/true);
+        return ModuleLoadResult::ConfigMismatch;
       }
 
       getDiagnostics().Report(ModuleNameLoc, diag::err_module_build_disabled)
@@ -1461,19 +1596,50 @@ CompilerInstance::loadModule(SourceLocation ImportLoc,
 
     llvm::Timer Timer;
     if (FrontendTimerGroup)
-      Timer.init("Loading " + ModuleFileName, *FrontendTimerGroup);
+      Timer.init("loading." + ModuleFileName, "Loading " + ModuleFileName,
+                 *FrontendTimerGroup);
     llvm::TimeRegion TimeLoading(FrontendTimerGroup ? &Timer : nullptr);
 
-    // Try to load the module file.
-    unsigned ARRFlags = ASTReader::ARR_OutOfDate | ASTReader::ARR_Missing;
+    // Try to load the module file. If we are trying to load from the prebuilt
+    // module path, we don't have the module map files and don't know how to
+    // rebuild modules.
+    unsigned ARRFlags = LoadFromPrebuiltModulePath ?
+                        ASTReader::ARR_ConfigurationMismatch :
+                        ASTReader::ARR_OutOfDate | ASTReader::ARR_Missing;
     switch (ModuleManager->ReadAST(ModuleFileName,
+                                   LoadFromPrebuiltModulePath ?
+                                   serialization::MK_PrebuiltModule :
                                    serialization::MK_ImplicitModule,
-                                   ImportLoc, ARRFlags)) {
-    case ASTReader::Success:
+                                   ImportLoc,
+                                   ARRFlags)) {
+    case ASTReader::Success: {
+      if (LoadFromPrebuiltModulePath && !Module) {
+        Module = PP->getHeaderSearchInfo().lookupModule(ModuleName);
+        if (!Module || !Module->getASTFile() ||
+            FileMgr->getFile(ModuleFileName) != Module->getASTFile()) {
+          // Error out if Module does not refer to the file in the prebuilt
+          // module path.
+          getDiagnostics().Report(ModuleNameLoc, diag::err_module_prebuilt)
+              << ModuleName;
+          ModuleBuildFailed = true;
+          KnownModules[Path[0].first] = nullptr;
+          return ModuleLoadResult();
+        }
+      }
       break;
+    }
 
     case ASTReader::OutOfDate:
     case ASTReader::Missing: {
+      if (LoadFromPrebuiltModulePath) {
+        // We can't rebuild the module without a module map. Since ReadAST
+        // already produces diagnostics for these two cases, we simply
+        // error out here.
+        ModuleBuildFailed = true;
+        KnownModules[Path[0].first] = nullptr;
+        return ModuleLoadResult();
+      }
+
       // The module file is missing or out-of-date. Build it.
       assert(Module && "missing module file");
       // Check whether there is a cycle in the module graph.
@@ -1524,8 +1690,13 @@ CompilerInstance::loadModule(SourceLocation ImportLoc,
       break;
     }
 
-    case ASTReader::VersionMismatch:
     case ASTReader::ConfigurationMismatch:
+      if (LoadFromPrebuiltModulePath)
+        getDiagnostics().Report(SourceLocation(),
+                                diag::warn_module_config_mismatch)
+            << ModuleFileName;
+      // Fall through to error out.
+    case ASTReader::VersionMismatch:
     case ASTReader::HadErrors:
       ModuleLoader::HadFatalFailure = true;
       // FIXME: The ASTReader will already have complained, but can we shoehorn
@@ -1617,7 +1788,7 @@ CompilerInstance::loadModule(SourceLocation ImportLoc,
         << Module->getFullModuleName()
         << SourceRange(Path.front().second, Path.back().second);
 
-      return ModuleLoadResult(nullptr, true);
+      return ModuleLoadResult::MissingExpected;
     }
 
     // Check whether this module is available.
@@ -1651,7 +1822,7 @@ CompilerInstance::loadModule(SourceLocation ImportLoc,
   }
 
   LastModuleImportLoc = ImportLoc;
-  LastModuleImportResult = ModuleLoadResult(Module, false);
+  LastModuleImportResult = ModuleLoadResult(Module);
   return LastModuleImportResult;
 }
 
@@ -1749,3 +1920,8 @@ CompilerInstance::lookupMissingImports(StringRef Name,
   return false;
 }
 void CompilerInstance::resetAndLeakSema() { BuryPointer(takeSema()); }
+
+void CompilerInstance::setExternalSemaSource(
+    IntrusiveRefCntPtr<ExternalSemaSource> ESS) {
+  ExternalSemaSrc = std::move(ESS);
+}