Merge clang, llvm, lld, lldb, compiler-rt and libc++ 5.0.0 release.

MFC r309126 (by emaste):

  Correct lld llvm-tblgen dependency file name

MFC r309169:

  Get rid of separate Subversion mergeinfo properties for llvm-dwarfdump
  and llvm-lto.  The mergeinfo confuses Subversion enormously, and these
  directories will just use the mergeinfo for llvm itself.

MFC r312765:

  Pull in r276136 from upstream llvm trunk (by Wei Mi):

    Use ValueOffsetPair to enhance value reuse during SCEV expansion.

    In D12090, the ExprValueMap was added to reuse existing value during
    SCEV expansion. However, const folding and sext/zext distribution can
    make the reuse still difficult.

    A simplified case is: suppose we know S1 expands to V1 in
    ExprValueMap, and
      S1 = S2 + C_a
      S3 = S2 + C_b
    where C_a and C_b are different SCEVConstants. Then we'd like to
    expand S3 as V1 - C_a + C_b instead of expanding S2 literally. It is
    helpful when S2 is a complex SCEV expr and S2 has no entry in
    ExprValueMap, which is usually caused by the fact that S3 is
    generated from S1 after const folding.

    In order to do that, we represent ExprValueMap as a mapping from SCEV
    to ValueOffsetPair. We will save both S1->{V1, 0} and S2->{V1, C_a}
    into the ExprValueMap when we create SCEV for V1. When S3 is
    expanded, it will first expand S2 to V1 - C_a because of S2->{V1,
    C_a} in the map, then expand S3 to V1 - C_a + C_b.

    Differential Revision: https://reviews.llvm.org/D21313

  This should fix assertion failures when building OpenCV >= 3.1.

  PR:		215649

MFC r312831:

  Revert r312765 for now, since it causes assertions when building
  lang/spidermonkey24.

  Reported by:	antoine
  PR:		215649

MFC r316511 (by jhb):

  Add an implementation of __ffssi2() derived from __ffsdi2().

  Newer versions of GCC include an __ffssi2() symbol in libgcc and the
  compiler can emit calls to it in generated code.  This is true for at
  least GCC 6.2 when compiling world for mips and mips64.

  Reviewed by:	jmallett, dim
  Sponsored by:	DARPA / AFRL
  Differential Revision:	https://reviews.freebsd.org/D10086

MFC r318601 (by adrian):

  [libcompiler-rt] add bswapdi2/bswapsi2

  This is required for mips gcc 6.3 userland to build/run.

  Reviewed by:	emaste, dim
  Approved by:	emaste
  Differential Revision:	https://reviews.freebsd.org/D10838

MFC r318884 (by emaste):

  lldb: map TRAP_CAP to a trace trap

  In the absense of a more specific handler for TRAP_CAP (generated by
  ENOTCAPABLE or ECAPMODE while in capability mode) treat it as a trace
  trap.

  Example usage (testing the bug in PR219173):

  % proccontrol -m trapcap lldb usr.bin/hexdump/obj/hexdump -- -Cv -s 1 /bin/ls
  ...
  (lldb) run
  Process 12980 launching
  Process 12980 launched: '.../usr.bin/hexdump/obj/hexdump' (x86_64)
  Process 12980 stopped
  * thread #1, stop reason = trace
      frame #0: 0x0000004b80c65f1a libc.so.7`__sys_lseek + 10
  ...

  In the future we should have LLDB control the trapcap procctl itself
  (as it does with ASLR), as well as report a specific stop reason.
  This change eliminates an assertion failure from LLDB for now.

MFC r319796:

  Remove a few unneeded files from libllvm, libclang and liblldb.

MFC r319885 (by emaste):

  lld: ELF: Fix ICF crash on absolute symbol relocations.

  If two sections contained relocations to absolute symbols with the same
  value we would crash when trying to access their sections. Add a check that
  both symbols point to sections before accessing their sections, and treat
  absolute symbols as equal if their values are equal.

  Obtained from:	LLD commit r292578

MFC r319918:

  Revert r319796 for now, it can cause undefined references when linking
  in some circumstances.

  Reported by:	Shawn Webb <shawn.webb@hardenedbsd.org>

MFC r319957 (by emaste):

  lld: Add armelf emulation mode

  Obtained from:	LLD r305375

MFC r321369:

  Upgrade our copies of clang, llvm, lld, lldb, compiler-rt and libc++ to
  5.0.0 (trunk r308421).  Upstream has branched for the 5.0.0 release,
  which should be in about a month.  Please report bugs and regressions,
  so we can get them into the release.

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

MFC r321420:

  Add a few more object files to liblldb, which should solve errors when
  linking the lldb executable in some cases.  In particular, when the
  -ffunction-sections -fdata-sections options are turned off, or
  ineffective.

  Reported by:	Shawn Webb, Mark Millard

MFC r321433:

  Cleanup stale Options.inc files from the previous libllvm build for
  clang 4.0.0.  Otherwise, these can get included before the two newly
  generated ones (which are different) for clang 5.0.0.

  Reported by:	Mark Millard

MFC r321439 (by bdrewery):

  Move llvm Options.inc hack from r321433 for NO_CLEAN to lib/clang/libllvm.

  The files are only ever generated to .OBJDIR, not to WORLDTMP (as a
  sysroot) and are only ever included from a compilation.  So using
  a beforebuild target here removes the file before the compilation
  tries to include it.

MFC r321664:

  Pull in r308891 from upstream llvm trunk (by Benjamin Kramer):

    [CodeGenPrepare] Cut off FindAllMemoryUses if there are too many uses.

    This avoids excessive compile time. The case I'm looking at is
    Function.cpp from an old version of LLVM that still had the giant
    memcmp string matcher in it. Before r308322 this compiled in about 2
    minutes, after it, clang takes infinite* time to compile it. With
    this patch we're at 5 min, which is still bad but this is a
    pathological case.

    The cut off at 20 uses was chosen by looking at other cut-offs in LLVM
    for user scanning. It's probably too high, but does the job and is
    very unlikely to regress anything.

    Fixes PR33900.

    * I'm impatient and aborted after 15 minutes, on the bug report it was
      killed after 2h.

  Pull in r308986 from upstream llvm trunk (by Simon Pilgrim):

    [X86][CGP] Reduce memcmp() expansion to 2 load pairs (PR33914)

    D35067/rL308322 attempted to support up to 4 load pairs for memcmp
    inlining which resulted in regressions for some optimized libc memcmp
    implementations (PR33914).

    Until we can match these more optimal cases, this patch reduces the
    memcmp expansion to a maximum of 2 load pairs (which matches what we
    do for -Os).

    This patch should be considered for the 5.0.0 release branch as well

    Differential Revision: https://reviews.llvm.org/D35830

  These fix a hang (or extremely long compile time) when building older
  LLVM ports.

  Reported by:    antoine
  PR:             219139

MFC r321719:

  Pull in r309503 from upstream clang trunk (by Richard Smith):

    PR33902: Invalidate line number cache when adding more text to
    existing buffer.

    This led to crashes as the line number cache would report a bogus
    line number for a line of code, and we'd try to find a nonexistent
    column within the line when printing diagnostics.

  This fixes an assertion when building the graphics/champlain port.

  Reported by:	antoine, kwm
  PR:		219139

MFC r321723:

  Upgrade our copies of clang, llvm, lld and lldb to r309439 from the
  upstream release_50 branch.  This is just after upstream's 5.0.0-rc1.

MFC r322320:

  Upgrade our copies of clang, llvm and libc++ to r310316 from the
  upstream release_50 branch.

MFC r322326 (by emaste):

  lldb: Make i386-*-freebsd expression work on JIT path

  * Enable i386 ABI creation for freebsd
  * Added an extra argument in ABISysV_i386::PrepareTrivialCall for mmap
    syscall
  * Unlike linux, the last argument of mmap is actually 64-bit(off_t).
    This requires us to push an additional word for the higher order bits.
  * Prior to this change, ktrace dump will show mmap failures due to
    invalid argument coming from the 6th mmap argument.

  Submitted by:	Karnajit Wangkhem
  Differential Revision:	https://reviews.llvm.org/D34776

MFC r322360 (by emaste):

  lldb: Report inferior signals as signals, not exceptions, on FreeBSD

  This is the FreeBSD equivalent of LLVM r238549.

  This serves 2 purposes:

  * LLDB should handle inferior process signals SIGSEGV/SIGILL/SIGBUS/
    SIGFPE the way it is suppose to be handled. Prior to this fix these
    signals will neither create a coredump, nor exit from the debugger
    or work for signal handling scenario.
  * eInvalidCrashReason need not report "unknown crash reason" if we have
    a valid si_signo

  llvm.org/pr23699

  Patch by Karnajit Wangkhem

  Differential Revision:  https://reviews.llvm.org/D35223

  Submitted by:	Karnajit Wangkhem
  Obtained from:	LLVM r310591

MFC r322474 (by emaste):

  lld: Add `-z muldefs` option.

  Obtained from:	LLVM r310757

MFC r322740:

  Upgrade our copies of clang, llvm, lld and libc++ to r311219 from the
  upstream release_50 branch.

MFC r322855:

  Upgrade our copies of clang, llvm, lldb and compiler-rt to r311606 from
  the upstream release_50 branch.

  As of this version, lib/msun's trig test should also work correctly
  again (see bug 220989 for more information).

  PR:		220989

MFC r323112:

  Upgrade our copies of clang, llvm, lldb and compiler-rt to r312293 from
  the upstream release_50 branch.  This corresponds to 5.0.0 rc4.

  As of this version, the cad/stepcode port should now compile in a more
  reasonable time on i386 (see bug 221836 for more information).

  PR:		221836

MFC r323245:

  Upgrade our copies of clang, llvm, lld, lldb, compiler-rt and libc++ to
  5.0.0 release (upstream r312559).

  Release notes for llvm, clang and lld will be available here soon:
  <http://releases.llvm.org/5.0.0/docs/ReleaseNotes.html>
  <http://releases.llvm.org/5.0.0/tools/clang/docs/ReleaseNotes.html>
  <http://releases.llvm.org/5.0.0/tools/lld/docs/ReleaseNotes.html>

  Relnotes:	yes

1 files changed, 244 insertions, 113 deletions

diff --git a/contrib/llvm/tools/clang/lib/Frontend/CompilerInstance.cpp b/contrib/llvm/tools/clang/lib/Frontend/CompilerInstance.cpp
index afcaa6e..bb6a665 100644
--- a/contrib/llvm/tools/clang/lib/Frontend/CompilerInstance.cpp
+++ b/contrib/llvm/tools/clang/lib/Frontend/CompilerInstance.cpp
@@ -11,8 +11,10 @@
 #include "clang/AST/ASTConsumer.h"
 #include "clang/AST/ASTContext.h"
 #include "clang/AST/Decl.h"
+#include "clang/Basic/CharInfo.h"
 #include "clang/Basic/Diagnostic.h"
 #include "clang/Basic/FileManager.h"
+#include "clang/Basic/MemoryBufferCache.h"
 #include "clang/Basic/SourceManager.h"
 #include "clang/Basic/TargetInfo.h"
 #include "clang/Basic/Version.h"
@@ -55,12 +57,15 @@ using namespace clang;
 
 CompilerInstance::CompilerInstance(
     std::shared_ptr<PCHContainerOperations> PCHContainerOps,
-    bool BuildingModule)
-    : ModuleLoader(BuildingModule), Invocation(new CompilerInvocation()),
-      ModuleManager(nullptr),
-      ThePCHContainerOperations(std::move(PCHContainerOps)),
-      BuildGlobalModuleIndex(false), HaveFullGlobalModuleIndex(false),
-      ModuleBuildFailed(false) {}
+    MemoryBufferCache *SharedPCMCache)
+    : ModuleLoader(/* BuildingModule = */ SharedPCMCache),
+      Invocation(new CompilerInvocation()),
+      PCMCache(SharedPCMCache ? SharedPCMCache : new MemoryBufferCache),
+      ThePCHContainerOperations(std::move(PCHContainerOps)) {
+  // Don't allow this to invalidate buffers in use by others.
+  if (SharedPCMCache)
+    getPCMCache().finalizeCurrentBuffers();
+}
 
 CompilerInstance::~CompilerInstance() {
   assert(OutputFiles.empty() && "Still output files in flight?");
@@ -131,6 +136,8 @@ IntrusiveRefCntPtr<ASTReader> CompilerInstance::getModuleManager() const {
   return ModuleManager;
 }
 void CompilerInstance::setModuleManager(IntrusiveRefCntPtr<ASTReader> Reader) {
+  assert(PCMCache.get() == &Reader->getModuleManager().getPCMCache() &&
+         "Expected ASTReader to use the same PCM cache");
   ModuleManager = std::move(Reader);
 }
 
@@ -373,7 +380,7 @@ void CompilerInstance::createPreprocessor(TranslationUnitKind TUKind) {
                        getDiagnostics(), getLangOpts(), &getTarget());
   PP = std::make_shared<Preprocessor>(
       Invocation->getPreprocessorOptsPtr(), getDiagnostics(), getLangOpts(),
-      getSourceManager(), *HeaderInfo, *this, PTHMgr,
+      getSourceManager(), getPCMCache(), *HeaderInfo, *this, PTHMgr,
       /*OwnsHeaderSearch=*/true, TUKind);
   PP->Initialize(getTarget(), getAuxTarget());
 
@@ -491,6 +498,8 @@ void CompilerInstance::createPCHExternalASTSource(
       AllowPCHWithCompilerErrors, getPreprocessor(), getASTContext(),
       getPCHContainerReader(),
       getFrontendOpts().ModuleFileExtensions,
+      TheDependencyFileGenerator.get(),
+      DependencyCollectors,
       DeserializationListener,
       OwnDeserializationListener, Preamble,
       getFrontendOpts().UseGlobalModuleIndex);
@@ -501,12 +510,14 @@ IntrusiveRefCntPtr<ASTReader> CompilerInstance::createPCHExternalASTSource(
     bool AllowPCHWithCompilerErrors, Preprocessor &PP, ASTContext &Context,
     const PCHContainerReader &PCHContainerRdr,
     ArrayRef<std::shared_ptr<ModuleFileExtension>> Extensions,
+    DependencyFileGenerator *DependencyFile,
+    ArrayRef<std::shared_ptr<DependencyCollector>> DependencyCollectors,
     void *DeserializationListener, bool OwnDeserializationListener,
     bool Preamble, bool UseGlobalModuleIndex) {
   HeaderSearchOptions &HSOpts = PP.getHeaderSearchInfo().getHeaderSearchOpts();
 
   IntrusiveRefCntPtr<ASTReader> Reader(new ASTReader(
-      PP, Context, PCHContainerRdr, Extensions,
+      PP, &Context, PCHContainerRdr, Extensions,
       Sysroot.empty() ? "" : Sysroot.data(), DisablePCHValidation,
       AllowPCHWithCompilerErrors, /*AllowConfigurationMismatch*/ false,
       HSOpts.ModulesValidateSystemHeaders, UseGlobalModuleIndex));
@@ -518,6 +529,12 @@ IntrusiveRefCntPtr<ASTReader> CompilerInstance::createPCHExternalASTSource(
   Reader->setDeserializationListener(
       static_cast<ASTDeserializationListener *>(DeserializationListener),
       /*TakeOwnership=*/OwnDeserializationListener);
+
+  if (DependencyFile)
+    DependencyFile->AttachToASTReader(*Reader);
+  for (auto &Listener : DependencyCollectors)
+    Listener->attachToASTReader(*Reader);
+
   switch (Reader->ReadAST(Path,
                           Preamble ? serialization::MK_Preamble
                                    : serialization::MK_PCH,
@@ -651,6 +668,11 @@ void CompilerInstance::clearOutputFiles(bool EraseFiles) {
       llvm::sys::fs::remove(OF.Filename);
   }
   OutputFiles.clear();
+  if (DeleteBuiltModules) {
+    for (auto &Module : BuiltModules)
+      llvm::sys::fs::remove(Module.second);
+    BuiltModules.clear();
+  }
   NonSeekStream.reset();
 }
 
@@ -803,8 +825,11 @@ bool CompilerInstance::InitializeSourceManager(
     const FrontendInputFile &Input, DiagnosticsEngine &Diags,
     FileManager &FileMgr, SourceManager &SourceMgr, HeaderSearch *HS,
     DependencyOutputOptions &DepOpts, const FrontendOptions &Opts) {
-  SrcMgr::CharacteristicKind
-    Kind = Input.isSystem() ? SrcMgr::C_System : SrcMgr::C_User;
+  SrcMgr::CharacteristicKind Kind =
+      Input.getKind().getFormat() == InputKind::ModuleMap
+          ? Input.isSystem() ? SrcMgr::C_System_ModuleMap
+                             : SrcMgr::C_User_ModuleMap
+          : Input.isSystem() ? SrcMgr::C_System : SrcMgr::C_User;
 
   if (Input.isBuffer()) {
     SourceMgr.setMainFileID(SourceMgr.createFileID(
@@ -842,7 +867,8 @@ bool CompilerInstance::InitializeSourceManager(
                             /*SearchPath=*/nullptr,
                             /*RelativePath=*/nullptr,
                             /*RequestingModule=*/nullptr,
-                            /*SuggestedModule=*/nullptr, /*SkipCache=*/true);
+                            /*SuggestedModule=*/nullptr, /*IsMapped=*/nullptr,
+                            /*SkipCache=*/true);
       // Also add the header to /showIncludes output.
       if (File)
         DepOpts.ShowIncludesPretendHeader = File->getName();
@@ -910,8 +936,9 @@ bool CompilerInstance::ExecuteAction(FrontendAction &Act) {
   if (!hasTarget())
     return false;
 
-  // Create TargetInfo for the other side of CUDA compilation.
-  if (getLangOpts().CUDA && !getFrontendOpts().AuxTriple.empty()) {
+  // Create TargetInfo for the other side of CUDA and OpenMP compilation.
+  if ((getLangOpts().CUDA || getLangOpts().OpenMPIsDevice) &&
+      !getFrontendOpts().AuxTriple.empty()) {
     auto TO = std::make_shared<TargetOptions>();
     TO->Triple = getFrontendOpts().AuxTriple;
     TO->HostTriple = getTarget().getTriple().str();
@@ -999,26 +1026,27 @@ bool CompilerInstance::ExecuteAction(FrontendAction &Act) {
 
 /// \brief Determine the appropriate source input kind based on language
 /// options.
-static InputKind getSourceInputKindFromOptions(const LangOptions &LangOpts) {
+static InputKind::Language getLanguageFromOptions(const LangOptions &LangOpts) {
   if (LangOpts.OpenCL)
-    return IK_OpenCL;
+    return InputKind::OpenCL;
   if (LangOpts.CUDA)
-    return IK_CUDA;
+    return InputKind::CUDA;
   if (LangOpts.ObjC1)
-    return LangOpts.CPlusPlus? IK_ObjCXX : IK_ObjC;
-  return LangOpts.CPlusPlus? IK_CXX : IK_C;
+    return LangOpts.CPlusPlus ? InputKind::ObjCXX : InputKind::ObjC;
+  return LangOpts.CPlusPlus ? InputKind::CXX : InputKind::C;
 }
 
 /// \brief Compile a module file for the given module, using the options 
 /// provided by the importing compiler instance. Returns true if the module
 /// was built without errors.
-static bool compileModuleImpl(CompilerInstance &ImportingInstance,
-                              SourceLocation ImportLoc,
-                              Module *Module,
-                              StringRef ModuleFileName) {
-  ModuleMap &ModMap 
-    = ImportingInstance.getPreprocessor().getHeaderSearchInfo().getModuleMap();
-    
+static bool
+compileModuleImpl(CompilerInstance &ImportingInstance, SourceLocation ImportLoc,
+                  StringRef ModuleName, FrontendInputFile Input,
+                  StringRef OriginalModuleMapFile, StringRef ModuleFileName,
+                  llvm::function_ref<void(CompilerInstance &)> PreBuildStep =
+                      [](CompilerInstance &) {},
+                  llvm::function_ref<void(CompilerInstance &)> PostBuildStep =
+                      [](CompilerInstance &) {}) {
   // Construct a compiler invocation for creating this module.
   auto Invocation =
       std::make_shared<CompilerInvocation>(ImportingInstance.getInvocation());
@@ -1032,7 +1060,7 @@ static bool compileModuleImpl(CompilerInstance &ImportingInstance,
 
   // Remove any macro definitions that are explicitly ignored by the module.
   // They aren't supposed to affect how the module is built anyway.
-  const HeaderSearchOptions &HSOpts = Invocation->getHeaderSearchOpts();
+  HeaderSearchOptions &HSOpts = Invocation->getHeaderSearchOpts();
   PPOpts.Macros.erase(
       std::remove_if(PPOpts.Macros.begin(), PPOpts.Macros.end(),
                      [&HSOpts](const std::pair<std::string, bool> &def) {
@@ -1043,7 +1071,7 @@ static bool compileModuleImpl(CompilerInstance &ImportingInstance,
       PPOpts.Macros.end());
 
   // Note the name of the module we're building.
-  Invocation->getLangOpts()->CurrentModule = Module->getTopLevelModuleName();
+  Invocation->getLangOpts()->CurrentModule = ModuleName;
 
   // Make sure that the failed-module structure has been allocated in
   // the importing instance, and propagate the pointer to the newly-created
@@ -1063,8 +1091,10 @@ static bool compileModuleImpl(CompilerInstance &ImportingInstance,
   FrontendOpts.DisableFree = false;
   FrontendOpts.GenerateGlobalModuleIndex = false;
   FrontendOpts.BuildingImplicitModule = true;
-  FrontendOpts.Inputs.clear();
-  InputKind IK = getSourceInputKindFromOptions(*Invocation->getLangOpts());
+  FrontendOpts.OriginalModuleMap = OriginalModuleMapFile;
+  // Force implicitly-built modules to hash the content of the module file.
+  HSOpts.ModulesHashContent = true;
+  FrontendOpts.Inputs = {Input};
 
   // Don't free the remapped file buffers; they are owned by our caller.
   PPOpts.RetainRemappedFileBuffers = true;
@@ -1074,9 +1104,11 @@ static bool compileModuleImpl(CompilerInstance &ImportingInstance,
          Invocation->getModuleHash() && "Module hash mismatch!");
   
   // Construct a compiler instance that will be used to actually create the
-  // module.
+  // module.  Since we're sharing a PCMCache,
+  // CompilerInstance::CompilerInstance is responsible for finalizing the
+  // buffers to prevent use-after-frees.
   CompilerInstance Instance(ImportingInstance.getPCHContainerOperations(),
-                            /*BuildingModule=*/true);
+                            &ImportingInstance.getPreprocessor().getPCMCache());
   auto &Inv = *Invocation;
   Instance.setInvocation(std::move(Invocation));
 
@@ -1093,7 +1125,7 @@ static bool compileModuleImpl(CompilerInstance &ImportingInstance,
   SourceManager &SourceMgr = Instance.getSourceManager();
   SourceMgr.setModuleBuildStack(
     ImportingInstance.getSourceManager().getModuleBuildStack());
-  SourceMgr.pushModuleBuildStack(Module->getTopLevelModuleName(),
+  SourceMgr.pushModuleBuildStack(ModuleName,
     FullSourceLoc(ImportLoc, ImportingInstance.getSourceManager()));
 
   // If we're collecting module dependencies, we need to share a collector
@@ -1102,47 +1134,28 @@ static bool compileModuleImpl(CompilerInstance &ImportingInstance,
   Instance.setModuleDepCollector(ImportingInstance.getModuleDepCollector());
   Inv.getDependencyOutputOpts() = DependencyOutputOptions();
 
-  // Get or create the module map that we'll use to build this module.
-  std::string InferredModuleMapContent;
-  if (const FileEntry *ModuleMapFile =
-          ModMap.getContainingModuleMapFile(Module)) {
-    // Use the module map where this module resides.
-    FrontendOpts.Inputs.emplace_back(ModuleMapFile->getName(), IK);
-  } else {
-    SmallString<128> FakeModuleMapFile(Module->Directory->getName());
-    llvm::sys::path::append(FakeModuleMapFile, "__inferred_module.map");
-    FrontendOpts.Inputs.emplace_back(FakeModuleMapFile, IK);
-
-    llvm::raw_string_ostream OS(InferredModuleMapContent);
-    Module->print(OS);
-    OS.flush();
-
-    std::unique_ptr<llvm::MemoryBuffer> ModuleMapBuffer =
-        llvm::MemoryBuffer::getMemBuffer(InferredModuleMapContent);
-    ModuleMapFile = Instance.getFileManager().getVirtualFile(
-        FakeModuleMapFile, InferredModuleMapContent.size(), 0);
-    SourceMgr.overrideFileContents(ModuleMapFile, std::move(ModuleMapBuffer));
-  }
-
-  // Construct a module-generating action. Passing through the module map is
-  // safe because the FileManager is shared between the compiler instances.
-  GenerateModuleFromModuleMapAction CreateModuleAction(
-      ModMap.getModuleMapFileForUniquing(Module), Module->IsSystem);
-
   ImportingInstance.getDiagnostics().Report(ImportLoc,
                                             diag::remark_module_build)
-    << Module->Name << ModuleFileName;
+    << ModuleName << ModuleFileName;
+
+  PreBuildStep(Instance);
 
   // Execute the action to actually build the module in-place. Use a separate
   // thread so that we get a stack large enough.
   const unsigned ThreadStackSize = 8 << 20;
   llvm::CrashRecoveryContext CRC;
-  CRC.RunSafelyOnThread([&]() { Instance.ExecuteAction(CreateModuleAction); },
-                        ThreadStackSize);
+  CRC.RunSafelyOnThread(
+      [&]() {
+        GenerateModuleFromModuleMapAction Action;
+        Instance.ExecuteAction(Action);
+      },
+      ThreadStackSize);
+
+  PostBuildStep(Instance);
 
   ImportingInstance.getDiagnostics().Report(ImportLoc,
                                             diag::remark_module_build_done)
-    << Module->Name;
+    << ModuleName;
 
   // Delete the temporary module map file.
   // FIXME: Even though we're executing under crash protection, it would still
@@ -1150,13 +1163,66 @@ static bool compileModuleImpl(CompilerInstance &ImportingInstance,
   // doesn't make sense for all clients, so clean this up manually.
   Instance.clearOutputFiles(/*EraseFiles=*/true);
 
+  return !Instance.getDiagnostics().hasErrorOccurred();
+}
+
+/// \brief Compile a module file for the given module, using the options 
+/// provided by the importing compiler instance. Returns true if the module
+/// was built without errors.
+static bool compileModuleImpl(CompilerInstance &ImportingInstance,
+                              SourceLocation ImportLoc,
+                              Module *Module,
+                              StringRef ModuleFileName) {
+  InputKind IK(getLanguageFromOptions(ImportingInstance.getLangOpts()),
+               InputKind::ModuleMap);
+
+  // Get or create the module map that we'll use to build this module.
+  ModuleMap &ModMap 
+    = ImportingInstance.getPreprocessor().getHeaderSearchInfo().getModuleMap();
+  bool Result;
+  if (const FileEntry *ModuleMapFile =
+          ModMap.getContainingModuleMapFile(Module)) {
+    // Use the module map where this module resides.
+    Result = compileModuleImpl(
+        ImportingInstance, ImportLoc, Module->getTopLevelModuleName(),
+        FrontendInputFile(ModuleMapFile->getName(), IK, +Module->IsSystem),
+        ModMap.getModuleMapFileForUniquing(Module)->getName(),
+        ModuleFileName);
+  } else {
+    // FIXME: We only need to fake up an input file here as a way of
+    // transporting the module's directory to the module map parser. We should
+    // be able to do that more directly, and parse from a memory buffer without
+    // inventing this file.
+    SmallString<128> FakeModuleMapFile(Module->Directory->getName());
+    llvm::sys::path::append(FakeModuleMapFile, "__inferred_module.map");
+
+    std::string InferredModuleMapContent;
+    llvm::raw_string_ostream OS(InferredModuleMapContent);
+    Module->print(OS);
+    OS.flush();
+
+    Result = compileModuleImpl(
+        ImportingInstance, ImportLoc, Module->getTopLevelModuleName(),
+        FrontendInputFile(FakeModuleMapFile, IK, +Module->IsSystem),
+        ModMap.getModuleMapFileForUniquing(Module)->getName(),
+        ModuleFileName,
+        [&](CompilerInstance &Instance) {
+      std::unique_ptr<llvm::MemoryBuffer> ModuleMapBuffer =
+          llvm::MemoryBuffer::getMemBuffer(InferredModuleMapContent);
+      ModuleMapFile = Instance.getFileManager().getVirtualFile(
+          FakeModuleMapFile, InferredModuleMapContent.size(), 0);
+      Instance.getSourceManager().overrideFileContents(
+          ModuleMapFile, std::move(ModuleMapBuffer));
+    });
+  }
+
   // We've rebuilt a module. If we're allowed to generate or update the global
   // module index, record that fact in the importing compiler instance.
   if (ImportingInstance.getFrontendOpts().GenerateGlobalModuleIndex) {
     ImportingInstance.setBuildGlobalModuleIndex(true);
   }
 
-  return !Instance.getDiagnostics().hasErrorOccurred();
+  return Result;
 }
 
 static bool compileAndLoadModule(CompilerInstance &ImportingInstance,
@@ -1180,10 +1246,14 @@ static bool compileAndLoadModule(CompilerInstance &ImportingInstance,
     llvm::LockFileManager Locked(ModuleFileName);
     switch (Locked) {
     case llvm::LockFileManager::LFS_Error:
-      Diags.Report(ModuleNameLoc, diag::err_module_lock_failure)
+      // PCMCache takes care of correctness and locks are only necessary for
+      // performance. Fallback to building the module in case of any lock
+      // related errors.
+      Diags.Report(ModuleNameLoc, diag::remark_module_lock_failure)
           << Module->Name << Locked.getErrorMessage();
-      return false;
-
+      // Clear out any potential leftover.
+      Locked.unsafeRemoveLockFile();
+      // FALLTHROUGH
     case llvm::LockFileManager::LFS_Owned:
       // We're responsible for building the module ourselves.
       if (!compileModuleImpl(ImportingInstance, ModuleNameLoc, Module,
@@ -1203,11 +1273,14 @@ static bool compileAndLoadModule(CompilerInstance &ImportingInstance,
       case llvm::LockFileManager::Res_OwnerDied:
         continue; // try again to get the lock.
       case llvm::LockFileManager::Res_Timeout:
-        Diags.Report(ModuleNameLoc, diag::err_module_lock_timeout)
+        // Since PCMCache takes care of correctness, we try waiting for another
+        // process to complete the build so clang does not do it done twice. If
+        // case of timeout, build it ourselves.
+        Diags.Report(ModuleNameLoc, diag::remark_module_lock_timeout)
             << Module->Name;
         // Clear the lock file so that future invokations can make progress.
         Locked.unsafeRemoveLockFile();
-        return false;
+        continue;
       }
       break;
     }
@@ -1400,7 +1473,7 @@ void CompilerInstance::createModuleManager() {
                                                  "Reading modules",
                                                  *FrontendTimerGroup);
     ModuleManager = new ASTReader(
-        getPreprocessor(), getASTContext(), getPCHContainerReader(),
+        getPreprocessor(), &getASTContext(), getPCHContainerReader(),
         getFrontendOpts().ModuleFileExtensions,
         Sysroot.empty() ? "" : Sysroot.c_str(), PPOpts.DisablePCHValidation,
         /*AllowASTWithCompilerErrors=*/false,
@@ -1555,24 +1628,36 @@ CompilerInstance::loadModule(SourceLocation ImportLoc,
         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.
+    enum ModuleSource {
+      ModuleNotFound, ModuleCache, PrebuiltModulePath, ModuleBuildPragma
+    } Source = ModuleNotFound;
+
+    // Check to see if the module has been built as part of this compilation
+    // via a module build pragma.
+    auto BuiltModuleIt = BuiltModules.find(ModuleName);
+    if (BuiltModuleIt != BuiltModules.end()) {
+      ModuleFileName = BuiltModuleIt->second;
+      Source = ModuleBuildPragma;
+    }
+
+    // Try to load the module from the prebuilt module path.
+    if (Source == ModuleNotFound && !HSOpts.PrebuiltModulePaths.empty()) {
       ModuleFileName = PP->getHeaderSearchInfo().getModuleFileName(
           ModuleName, "", /*UsePrebuiltPath*/ true);
       if (!ModuleFileName.empty())
-        LoadFromPrebuiltModulePath = true;
+        Source = PrebuiltModulePath;
     }
-    if (!LoadFromPrebuiltModulePath && Module) {
-      // Load the module from the module cache.
+
+    // Try to load the module from the module cache.
+    if (Source == ModuleNotFound && Module) {
       ModuleFileName = PP->getHeaderSearchInfo().getModuleFileName(Module);
-    } else if (!LoadFromPrebuiltModulePath) {
+      Source = ModuleCache;
+    }
+
+    if (Source == ModuleNotFound) {
       // We can't find a module, error out here.
       getDiagnostics().Report(ModuleNameLoc, diag::err_module_not_found)
-      << ModuleName
-      << SourceRange(ImportLoc, ModuleNameLoc);
+          << ModuleName << SourceRange(ImportLoc, ModuleNameLoc);
       ModuleBuildFailed = true;
       return ModuleLoadResult();
     }
@@ -1600,20 +1685,20 @@ CompilerInstance::loadModule(SourceLocation ImportLoc,
                  *FrontendTimerGroup);
     llvm::TimeRegion TimeLoading(FrontendTimerGroup ? &Timer : nullptr);
 
-    // 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;
+    // Try to load the module file. If we are not trying to load from the
+    // module cache, we don't know how to rebuild modules.
+    unsigned ARRFlags = Source == ModuleCache ?
+                        ASTReader::ARR_OutOfDate | ASTReader::ARR_Missing :
+                        ASTReader::ARR_ConfigurationMismatch;
     switch (ModuleManager->ReadAST(ModuleFileName,
-                                   LoadFromPrebuiltModulePath ?
-                                   serialization::MK_PrebuiltModule :
-                                   serialization::MK_ImplicitModule,
-                                   ImportLoc,
-                                   ARRFlags)) {
+                                   Source == PrebuiltModulePath
+                                       ? serialization::MK_PrebuiltModule
+                                       : Source == ModuleBuildPragma
+                                             ? serialization::MK_ExplicitModule
+                                             : serialization::MK_ImplicitModule,
+                                   ImportLoc, ARRFlags)) {
     case ASTReader::Success: {
-      if (LoadFromPrebuiltModulePath && !Module) {
+      if (Source != ModuleCache && !Module) {
         Module = PP->getHeaderSearchInfo().lookupModule(ModuleName);
         if (!Module || !Module->getASTFile() ||
             FileMgr->getFile(ModuleFileName) != Module->getASTFile()) {
@@ -1631,10 +1716,10 @@ CompilerInstance::loadModule(SourceLocation ImportLoc,
 
     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.
+      if (Source != ModuleCache) {
+        // We don't know the desired configuration for this module and don't
+        // necessarily even have 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();
@@ -1691,11 +1776,14 @@ CompilerInstance::loadModule(SourceLocation ImportLoc,
     }
 
     case ASTReader::ConfigurationMismatch:
-      if (LoadFromPrebuiltModulePath)
+      if (Source == PrebuiltModulePath)
+        // FIXME: We shouldn't be setting HadFatalFailure below if we only
+        // produce a warning here!
         getDiagnostics().Report(SourceLocation(),
                                 diag::warn_module_config_mismatch)
             << ModuleFileName;
       // Fall through to error out.
+      LLVM_FALLTHROUGH;
     case ASTReader::VersionMismatch:
     case ASTReader::HadErrors:
       ModuleLoader::HadFatalFailure = true;
@@ -1719,7 +1807,7 @@ CompilerInstance::loadModule(SourceLocation ImportLoc,
   // If we never found the module, fail.
   if (!Module)
     return ModuleLoadResult();
-  
+
   // Verify that the rest of the module path actually corresponds to
   // a submodule.
   if (Path.size() > 1) {
@@ -1792,20 +1880,10 @@ CompilerInstance::loadModule(SourceLocation ImportLoc,
     }
 
     // Check whether this module is available.
-    clang::Module::Requirement Requirement;
-    clang::Module::UnresolvedHeaderDirective MissingHeader;
-    if (!Module->isAvailable(getLangOpts(), getTarget(), Requirement,
-                             MissingHeader)) {
-      if (MissingHeader.FileNameLoc.isValid()) {
-        getDiagnostics().Report(MissingHeader.FileNameLoc,
-                                diag::err_module_header_missing)
-          << MissingHeader.IsUmbrella << MissingHeader.FileName;
-      } else {
-        getDiagnostics().Report(ImportLoc, diag::err_module_unavailable)
-          << Module->getFullModuleName()
-          << Requirement.second << Requirement.first
-          << SourceRange(Path.front().second, Path.back().second);
-      }
+    if (Preprocessor::checkModuleIsAvailable(getLangOpts(), getTarget(),
+                                             getDiagnostics(), Module)) {
+      getDiagnostics().Report(ImportLoc, diag::note_module_import_here)
+        << SourceRange(Path.front().second, Path.back().second);
       LastModuleImportLoc = ImportLoc;
       LastModuleImportResult = ModuleLoadResult();
       return ModuleLoadResult();
@@ -1826,6 +1904,59 @@ CompilerInstance::loadModule(SourceLocation ImportLoc,
   return LastModuleImportResult;
 }
 
+void CompilerInstance::loadModuleFromSource(SourceLocation ImportLoc,
+                                            StringRef ModuleName,
+                                            StringRef Source) {
+  // Avoid creating filenames with special characters.
+  SmallString<128> CleanModuleName(ModuleName);
+  for (auto &C : CleanModuleName)
+    if (!isAlphanumeric(C))
+      C = '_';
+
+  // FIXME: Using a randomized filename here means that our intermediate .pcm
+  // output is nondeterministic (as .pcm files refer to each other by name).
+  // Can this affect the output in any way?
+  SmallString<128> ModuleFileName;
+  if (std::error_code EC = llvm::sys::fs::createTemporaryFile(
+          CleanModuleName, "pcm", ModuleFileName)) {
+    getDiagnostics().Report(ImportLoc, diag::err_fe_unable_to_open_output)
+        << ModuleFileName << EC.message();
+    return;
+  }
+  std::string ModuleMapFileName = (CleanModuleName + ".map").str();
+
+  FrontendInputFile Input(
+      ModuleMapFileName,
+      InputKind(getLanguageFromOptions(*Invocation->getLangOpts()),
+                InputKind::ModuleMap, /*Preprocessed*/true));
+
+  std::string NullTerminatedSource(Source.str());
+
+  auto PreBuildStep = [&](CompilerInstance &Other) {
+    // Create a virtual file containing our desired source.
+    // FIXME: We shouldn't need to do this.
+    const FileEntry *ModuleMapFile = Other.getFileManager().getVirtualFile(
+        ModuleMapFileName, NullTerminatedSource.size(), 0);
+    Other.getSourceManager().overrideFileContents(
+        ModuleMapFile,
+        llvm::MemoryBuffer::getMemBuffer(NullTerminatedSource.c_str()));
+
+    Other.BuiltModules = std::move(BuiltModules);
+    Other.DeleteBuiltModules = false;
+  };
+
+  auto PostBuildStep = [this](CompilerInstance &Other) {
+    BuiltModules = std::move(Other.BuiltModules);
+  };
+
+  // Build the module, inheriting any modules that we've built locally.
+  if (compileModuleImpl(*this, ImportLoc, ModuleName, Input, StringRef(),
+                        ModuleFileName, PreBuildStep, PostBuildStep)) {
+    BuiltModules[ModuleName] = ModuleFileName.str();
+    llvm::sys::RemoveFileOnSignal(ModuleFileName);
+  }
+}
+
 void CompilerInstance::makeModuleVisible(Module *Mod,
                                          Module::NameVisibilityKind Visibility,
                                          SourceLocation ImportLoc) {