Vendor import of lld trunk r290819:vendor/lld/lld-trunk-r290819

https://llvm.org/svn/llvm-project/lld/trunk@290819

806 files changed, 27950 insertions, 11087 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 46ca748f8fac..23cef2e9fc67 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,3 +1,54 @@
+# Check if lld is built as a standalone project.
+if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
+  project(lld)
+  cmake_minimum_required(VERSION 3.4.3)
+
+  set(CMAKE_INCLUDE_CURRENT_DIR ON)
+  set(LLD_BUILT_STANDALONE TRUE)
+
+  find_program(LLVM_CONFIG_PATH "llvm-config" DOC "Path to llvm-config binary")
+  if(NOT LLVM_CONFIG_PATH)
+    message(FATAL_ERROR "llvm-config not found: specify LLVM_CONFIG_PATH")
+  endif()
+
+  execute_process(COMMAND "${LLVM_CONFIG_PATH}" "--obj-root" "--includedir"
+                  RESULT_VARIABLE HAD_ERROR
+                  OUTPUT_VARIABLE LLVM_CONFIG_OUTPUT
+                  OUTPUT_STRIP_TRAILING_WHITESPACE)
+  if(HAD_ERROR)
+    message(FATAL_ERROR "llvm-config failed with status ${HAD_ERROR}")
+  endif()
+
+  string(REGEX REPLACE "[ \t]*[\r\n]+[ \t]*" ";" LLVM_CONFIG_OUTPUT "${LLVM_CONFIG_OUTPUT}")
+
+  list(GET LLVM_CONFIG_OUTPUT 0 OBJ_ROOT)
+  list(GET LLVM_CONFIG_OUTPUT 1 MAIN_INCLUDE_DIR)
+
+  set(LLVM_OBJ_ROOT ${OBJ_ROOT} CACHE PATH "path to LLVM build tree")
+  set(LLVM_MAIN_INCLUDE_DIR ${MAIN_INCLUDE_DIR} CACHE PATH "path to llvm/include")
+
+  file(TO_CMAKE_PATH ${LLVM_OBJ_ROOT} LLVM_BINARY_DIR)
+  set(LLVM_CMAKE_PATH "${LLVM_BINARY_DIR}/lib${LLVM_LIBDIR_SUFFIX}/cmake/llvm")
+
+  if(NOT EXISTS "${LLVM_CMAKE_PATH}/LLVMConfig.cmake")
+    message(FATAL_ERROR "LLVMConfig.cmake not found")
+  endif()
+  include("${LLVM_CMAKE_PATH}/LLVMConfig.cmake")
+
+  list(APPEND CMAKE_MODULE_PATH "${LLVM_CMAKE_PATH}")
+
+  set(PACKAGE_VERSION "${LLVM_PACKAGE_VERSION}")
+  include_directories("${LLVM_BINARY_DIR}/include" ${LLVM_INCLUDE_DIRS})
+  link_directories(${LLVM_LIBRARY_DIRS})
+
+  set(LLVM_RUNTIME_OUTPUT_INTDIR ${CMAKE_BINARY_DIR}/${CMAKE_CFG_INTDIR}/bin)
+  find_program(LLVM_TABLEGEN_EXE "llvm-tblgen" ${LLVM_TOOLS_BINARY_DIR} NO_DEFAULT_PATH)
+
+  include(AddLLVM)
+  include(TableGen)
+  include(HandleLLVMOptions)
+endif()
+
 set(LLD_SOURCE_DIR ${CMAKE_CURRENT_SOURCE_DIR})
 set(LLD_INCLUDE_DIR ${LLD_SOURCE_DIR}/include )
 set(LLD_BINARY_DIR ${CMAKE_CURRENT_BINARY_DIR})
@@ -55,6 +106,8 @@ endif()
 
 list (APPEND CMAKE_MODULE_PATH "${LLD_SOURCE_DIR}/cmake/modules")
 
+include(AddLLD)
+
 option(LLD_USE_VTUNE
        "Enable VTune user task tracking."
        OFF)
@@ -67,6 +120,8 @@ if (LLD_USE_VTUNE)
   endif()
 endif()
 
+option(LLD_BUILD_TOOLS
+  "Build the lld tools. If OFF, just generate build targets." ON)
 
 if (MSVC)
   add_definitions(-wd4530) # Suppress 'warning C4530: C++ exception handler used, but unwind semantics are not enabled.'
@@ -87,12 +142,6 @@ if (NOT LLVM_INSTALL_TOOLCHAIN_ONLY)
     )
 endif()
 
-macro(add_lld_library name)
-  add_llvm_library(${name} ${ARGN})
-  set_target_properties(${name} PROPERTIES FOLDER "lld libraries")
-endmacro(add_lld_library)
-
-
 add_subdirectory(lib)
 add_subdirectory(tools/lld)
 
diff --git a/COFF/CMakeLists.txt b/COFF/CMakeLists.txt
index ad5b6fda1693..70a33b9fdd81 100644
--- a/COFF/CMakeLists.txt
+++ b/COFF/CMakeLists.txt
@@ -2,6 +2,10 @@ set(LLVM_TARGET_DEFINITIONS Options.td)
 tablegen(LLVM Options.inc -gen-opt-parser-defs)
 add_public_tablegen_target(COFFOptionsTableGen)
 
+if(NOT LLD_BUILT_STANDALONE)
+  set(tablegen_deps intrinsics_gen)
+endif()
+
 add_lld_library(lldCOFF
   Chunks.cpp
   DLL.cpp
@@ -14,6 +18,7 @@ add_lld_library(lldCOFF
   MarkLive.cpp
   ModuleDef.cpp
   PDB.cpp
+  Strings.cpp
   SymbolTable.cpp
   Symbols.cpp
   Writer.cpp
@@ -21,6 +26,9 @@ add_lld_library(lldCOFF
   LINK_COMPONENTS
   ${LLVM_TARGETS_TO_BUILD}
   Core
+  DebugInfoCodeView
+  DebugInfoMSF
+  DebugInfoPDB
   LTO
   LibDriver
   Object
@@ -30,7 +38,11 @@ add_lld_library(lldCOFF
   Option
   Support
 
-  LINK_LIBS ${PTHREAD_LIB}
-  )
+  LINK_LIBS
+  lldCore
+  ${PTHREAD_LIB}
 
-add_dependencies(lldCOFF COFFOptionsTableGen intrinsics_gen)
+  DEPENDS
+  COFFOptionsTableGen
+  ${tablegen_deps}
+  )
diff --git a/COFF/Chunks.cpp b/COFF/Chunks.cpp
index 1c1b18176aa2..7f0dfa92ec10 100644
--- a/COFF/Chunks.cpp
+++ b/COFF/Chunks.cpp
@@ -28,7 +28,7 @@ namespace lld {
 namespace coff {
 
 SectionChunk::SectionChunk(ObjectFile *F, const coff_section *H)
-    : Chunk(SectionKind), Repl(this), File(F), Header(H),
+    : Chunk(SectionKind), Repl(this), Header(H), File(F),
       Relocs(File->getCOFFObj()->getRelocations(Header)),
       NumRelocs(std::distance(Relocs.begin(), Relocs.end())) {
   // Initialize SectionName.
@@ -81,11 +81,23 @@ void SectionChunk::applyRelX86(uint8_t *Off, uint16_t Type, Defined *Sym,
 }
 
 static void applyMOV(uint8_t *Off, uint16_t V) {
-  or16(Off, ((V & 0x800) >> 1) | ((V >> 12) & 0xf));
-  or16(Off + 2, ((V & 0x700) << 4) | (V & 0xff));
+  write16le(Off, (read16le(Off) & 0xfbf0) | ((V & 0x800) >> 1) | ((V >> 12) & 0xf));
+  write16le(Off + 2, (read16le(Off + 2) & 0x8f00) | ((V & 0x700) << 4) | (V & 0xff));
+}
+
+static uint16_t readMOV(uint8_t *Off) {
+  uint16_t Opcode1 = read16le(Off);
+  uint16_t Opcode2 = read16le(Off + 2);
+  uint16_t Imm = (Opcode2 & 0x00ff) | ((Opcode2 >> 4) & 0x0700);
+  Imm |= ((Opcode1 << 1) & 0x0800) | ((Opcode1 & 0x000f) << 12);
+  return Imm;
 }
 
 static void applyMOV32T(uint8_t *Off, uint32_t V) {
+  uint16_t ImmW = readMOV(Off);     // read MOVW operand
+  uint16_t ImmT = readMOV(Off + 4); // read MOVT operand
+  uint32_t Imm = ImmW | (ImmT << 16);
+  V += Imm;                         // add the immediate offset
   applyMOV(Off, V);           // set MOVW operand
   applyMOV(Off + 4, V >> 16); // set MOVT operand
 }
@@ -99,11 +111,14 @@ static void applyBranch20T(uint8_t *Off, int32_t V) {
 }
 
 static void applyBranch24T(uint8_t *Off, int32_t V) {
+  if (!isInt<25>(V))
+    fatal("relocation out of range");
   uint32_t S = V < 0 ? 1 : 0;
   uint32_t J1 = ((~V >> 23) & 1) ^ S;
   uint32_t J2 = ((~V >> 22) & 1) ^ S;
   or16(Off, (S << 10) | ((V >> 12) & 0x3ff));
-  or16(Off + 2, (J1 << 13) | (J2 << 11) | ((V >> 1) & 0x7ff));
+  // Clear out the J1 and J2 bits which may be set.
+  write16le(Off + 2, (read16le(Off + 2) & 0xd000) | (J1 << 13) | (J2 << 11) | ((V >> 1) & 0x7ff));
 }
 
 void SectionChunk::applyRelARM(uint8_t *Off, uint16_t Type, Defined *Sym,
@@ -119,6 +134,7 @@ void SectionChunk::applyRelARM(uint8_t *Off, uint16_t Type, Defined *Sym,
   case IMAGE_REL_ARM_BRANCH20T: applyBranch20T(Off, S - P - 4); break;
   case IMAGE_REL_ARM_BRANCH24T: applyBranch24T(Off, S - P - 4); break;
   case IMAGE_REL_ARM_BLX23T:    applyBranch24T(Off, S - P - 4); break;
+  case IMAGE_REL_ARM_SECREL:    add32(Off, Sym->getSecrel()); break;
   default:
     fatal("unsupported relocation type");
   }
@@ -134,7 +150,7 @@ void SectionChunk::writeTo(uint8_t *Buf) const {
   // Apply relocations.
   for (const coff_relocation &Rel : Relocs) {
     uint8_t *Off = Buf + OutputSectionOff + Rel.VirtualAddress;
-    SymbolBody *Body = File->getSymbolBody(Rel.SymbolTableIndex)->repl();
+    SymbolBody *Body = File->getSymbolBody(Rel.SymbolTableIndex);
     Defined *Sym = cast<Defined>(Body);
     uint64_t P = RVA + Rel.VirtualAddress;
     switch (Config->Machine) {
@@ -187,7 +203,7 @@ void SectionChunk::getBaserels(std::vector<Baserel> *Res) {
     uint8_t Ty = getBaserelType(Rel);
     if (Ty == IMAGE_REL_BASED_ABSOLUTE)
       continue;
-    SymbolBody *Body = File->getSymbolBody(Rel.SymbolTableIndex)->repl();
+    SymbolBody *Body = File->getSymbolBody(Rel.SymbolTableIndex);
     if (isa<DefinedAbsolute>(Body))
       continue;
     Res->emplace_back(RVA + Rel.VirtualAddress, Ty);
@@ -210,7 +226,7 @@ void SectionChunk::printDiscardedMessage() const {
   // Removed by dead-stripping. If it's removed by ICF, ICF already
   // printed out the name, so don't repeat that here.
   if (Sym && this == Repl)
-    llvm::outs() << "Discarded " << Sym->getName() << "\n";
+    outs() << "Discarded " << Sym->getName() << "\n";
 }
 
 StringRef SectionChunk::getDebugName() {
@@ -233,7 +249,7 @@ void SectionChunk::replace(SectionChunk *Other) {
 CommonChunk::CommonChunk(const COFFSymbolRef S) : Sym(S) {
   // Common symbols are aligned on natural boundaries up to 32 bytes.
   // This is what MSVC link.exe does.
-  Align = std::min(uint64_t(32), NextPowerOf2(Sym.getValue()));
+  Align = std::min(uint64_t(32), PowerOf2Ceil(Sym.getValue()));
 }
 
 uint32_t CommonChunk::getPermissions() const {
diff --git a/COFF/Chunks.h b/COFF/Chunks.h
index cd0e2e69ef5d..59e36b84c9b0 100644
--- a/COFF/Chunks.h
+++ b/COFF/Chunks.h
@@ -17,7 +17,6 @@
 #include "llvm/ADT/iterator.h"
 #include "llvm/ADT/iterator_range.h"
 #include "llvm/Object/COFF.h"
-#include <atomic>
 #include <utility>
 #include <vector>
 
@@ -29,7 +28,6 @@ using llvm::object::COFFSymbolRef;
 using llvm::object::SectionRef;
 using llvm::object::coff_relocation;
 using llvm::object::coff_section;
-using llvm::sys::fs::file_magic;
 
 class Baserel;
 class Defined;
@@ -187,11 +185,12 @@ public:
   // Auxiliary Format 5: Section Definitions. Used for ICF.
   uint32_t Checksum = 0;
 
+  const coff_section *Header;
+
 private:
   // A file this chunk was created from.
   ObjectFile *File;
 
-  const coff_section *Header;
   StringRef SectionName;
   std::vector<SectionChunk *> AssocChildren;
   llvm::iterator_range<const coff_relocation *> Relocs;
@@ -202,7 +201,7 @@ private:
 
   // Used for ICF (Identical COMDAT Folding)
   void replace(SectionChunk *Other);
-  std::atomic<uint64_t> GroupID = { 0 };
+  uint32_t Color[2] = {0, 0};
 
   // Sym points to a section symbol if this is a COMDAT chunk.
   DefinedRegular *Sym = nullptr;
diff --git a/COFF/Config.h b/COFF/Config.h
index a5472e937fa1..0fa3338aa28c 100644
--- a/COFF/Config.h
+++ b/COFF/Config.h
@@ -26,7 +26,8 @@ using llvm::StringRef;
 class DefinedAbsolute;
 class DefinedRelative;
 class StringChunk;
-class Undefined;
+struct Symbol;
+class SymbolBody;
 
 // Short aliases.
 static const auto AMD64 = llvm::COFF::IMAGE_FILE_MACHINE_AMD64;
@@ -37,7 +38,7 @@ static const auto I386 = llvm::COFF::IMAGE_FILE_MACHINE_I386;
 struct Export {
   StringRef Name;       // N in /export:N or /export:E=N
   StringRef ExtName;    // E in /export:E=N
-  Undefined *Sym = nullptr;
+  SymbolBody *Sym = nullptr;
   uint16_t Ordinal = 0;
   bool Noname = false;
   bool Data = false;
@@ -61,6 +62,13 @@ struct Export {
   }
 };
 
+enum class DebugType {
+  None  = 0x0,
+  CV    = 0x1,  /// CodeView
+  PData = 0x2,  /// Procedure Data
+  Fixup = 0x4,  /// Relocation Table
+};
+
 // Global configuration.
 struct Configuration {
   enum ManifestKind { SideBySide, Embed, No };
@@ -69,7 +77,7 @@ struct Configuration {
   llvm::COFF::MachineTypes Machine = IMAGE_FILE_MACHINE_UNKNOWN;
   bool Verbose = false;
   WindowsSubsystem Subsystem = llvm::COFF::IMAGE_SUBSYSTEM_UNKNOWN;
-  Undefined *Entry = nullptr;
+  SymbolBody *Entry = nullptr;
   bool NoEntry = false;
   std::string OutputFile;
   bool DoGC = true;
@@ -78,9 +86,11 @@ struct Configuration {
   bool Force = false;
   bool Debug = false;
   bool WriteSymtab = true;
+  unsigned DebugTypes = static_cast<unsigned>(DebugType::None);
+  StringRef PDBPath;
 
   // Symbols in this set are considered as live by the garbage collector.
-  std::set<Undefined *> GCRoot;
+  std::set<SymbolBody *> GCRoot;
 
   std::set<StringRef> NoDefaultLibs;
   bool NoDefaultLibAll = false;
@@ -91,11 +101,11 @@ struct Configuration {
   std::vector<Export> Exports;
   std::set<std::string> DelayLoads;
   std::map<std::string, int> DLLOrder;
-  Undefined *DelayLoadHelper = nullptr;
+  SymbolBody *DelayLoadHelper = nullptr;
 
   // Used for SafeSEH.
-  DefinedRelative *SEHTable = nullptr;
-  DefinedAbsolute *SEHCount = nullptr;
+  Symbol *SEHTable = nullptr;
+  Symbol *SEHCount = nullptr;
 
   // Used for /opt:lldlto=N
   unsigned LTOOptLevel = 2;
@@ -141,6 +151,10 @@ struct Configuration {
   bool TerminalServerAware = true;
   bool LargeAddressAware = false;
   bool HighEntropyVA = false;
+
+  // This is for debugging.
+  bool DebugPdb = false;
+  bool DumpPdb = false;
 };
 
 extern Configuration *Config;
diff --git a/COFF/DLL.cpp b/COFF/DLL.cpp
index 9ac370c11d59..f93dc5cde44c 100644
--- a/COFF/DLL.cpp
+++ b/COFF/DLL.cpp
@@ -324,7 +324,7 @@ public:
       if (E.ForwardChunk) {
         write32le(P, E.ForwardChunk->getRVA());
       } else {
-        write32le(P, cast<Defined>(E.Sym->repl())->getRVA());
+        write32le(P, cast<Defined>(E.Sym)->getRVA());
       }
     }
   }
diff --git a/COFF/Driver.cpp b/COFF/Driver.cpp
index bb6a60e4fc4c..dc3a00ba55ed 100644
--- a/COFF/Driver.cpp
+++ b/COFF/Driver.cpp
@@ -7,15 +7,17 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "Config.h"
 #include "Driver.h"
+#include "Config.h"
 #include "Error.h"
 #include "InputFiles.h"
+#include "Memory.h"
 #include "SymbolTable.h"
 #include "Symbols.h"
 #include "Writer.h"
 #include "lld/Driver/Driver.h"
 #include "llvm/ADT/Optional.h"
+#include "llvm/ADT/StringSwitch.h"
 #include "llvm/LibDriver/LibDriver.h"
 #include "llvm/Option/Arg.h"
 #include "llvm/Option/ArgList.h"
@@ -28,6 +30,13 @@
 #include <algorithm>
 #include <memory>
 
+#ifdef _MSC_VER
+// <future> depends on <eh.h> for __uncaught_exception.
+#include <eh.h>
+#endif
+
+#include <future>
+
 using namespace llvm;
 using namespace llvm::COFF;
 using llvm::sys::Process;
@@ -41,11 +50,13 @@ namespace coff {
 Configuration *Config;
 LinkerDriver *Driver;
 
-bool link(llvm::ArrayRef<const char *> Args) {
-  Configuration C;
-  LinkerDriver D;
-  Config = &C;
-  Driver = &D;
+BumpPtrAllocator BAlloc;
+StringSaver Saver{BAlloc};
+std::vector<SpecificAllocBase *> SpecificAllocBase::Instances;
+
+bool link(ArrayRef<const char *> Args) {
+  Config = make<Configuration>();
+  Driver = make<LinkerDriver>();
   Driver->link(Args);
   return true;
 }
@@ -58,26 +69,123 @@ static std::string getOutputPath(StringRef Path) {
   return (S.substr(0, S.rfind('.')) + E).str();
 }
 
-// Opens a file. Path has to be resolved already.
-// Newly created memory buffers are owned by this driver.
-MemoryBufferRef LinkerDriver::openFile(StringRef Path) {
-  std::unique_ptr<MemoryBuffer> MB =
-      check(MemoryBuffer::getFile(Path), "could not open " + Path);
-  MemoryBufferRef MBRef = MB->getMemBufferRef();
-  OwningMBs.push_back(std::move(MB)); // take ownership
+// ErrorOr is not default constructible, so it cannot be used as the type
+// parameter of a future.
+// FIXME: We could open the file in createFutureForFile and avoid needing to
+// return an error here, but for the moment that would cost us a file descriptor
+// (a limited resource on Windows) for the duration that the future is pending.
+typedef std::pair<std::unique_ptr<MemoryBuffer>, std::error_code> MBErrPair;
+
+// Create a std::future that opens and maps a file using the best strategy for
+// the host platform.
+static std::future<MBErrPair> createFutureForFile(std::string Path) {
+#if LLVM_ON_WIN32
+  // On Windows, file I/O is relatively slow so it is best to do this
+  // asynchronously.
+  auto Strategy = std::launch::async;
+#else
+  auto Strategy = std::launch::deferred;
+#endif
+  return std::async(Strategy, [=]() {
+    auto MBOrErr = MemoryBuffer::getFile(Path);
+    if (!MBOrErr)
+      return MBErrPair{nullptr, MBOrErr.getError()};
+    return MBErrPair{std::move(*MBOrErr), std::error_code()};
+  });
+}
+
+MemoryBufferRef LinkerDriver::takeBuffer(std::unique_ptr<MemoryBuffer> MB) {
+  MemoryBufferRef MBRef = *MB;
+  OwningMBs.push_back(std::move(MB));
+
+  if (Driver->Cpio)
+    Driver->Cpio->append(relativeToRoot(MBRef.getBufferIdentifier()),
+                         MBRef.getBuffer());
+
   return MBRef;
 }
 
-static std::unique_ptr<InputFile> createFile(MemoryBufferRef MB) {
+void LinkerDriver::addBuffer(std::unique_ptr<MemoryBuffer> MB) {
+  MemoryBufferRef MBRef = takeBuffer(std::move(MB));
+
   // File type is detected by contents, not by file extension.
-  file_magic Magic = identify_magic(MB.getBuffer());
+  file_magic Magic = identify_magic(MBRef.getBuffer());
+  if (Magic == file_magic::windows_resource) {
+    Resources.push_back(MBRef);
+    return;
+  }
+
+  FilePaths.push_back(MBRef.getBufferIdentifier());
   if (Magic == file_magic::archive)
-    return std::unique_ptr<InputFile>(new ArchiveFile(MB));
+    return Symtab.addFile(make<ArchiveFile>(MBRef));
   if (Magic == file_magic::bitcode)
-    return std::unique_ptr<InputFile>(new BitcodeFile(MB));
+    return Symtab.addFile(make<BitcodeFile>(MBRef));
+  if (Magic == file_magic::coff_cl_gl_object)
+    fatal(MBRef.getBufferIdentifier() + ": is not a native COFF file. "
+          "Recompile without /GL");
+  Symtab.addFile(make<ObjectFile>(MBRef));
+}
+
+void LinkerDriver::enqueuePath(StringRef Path) {
+  auto Future =
+      std::make_shared<std::future<MBErrPair>>(createFutureForFile(Path));
+  std::string PathStr = Path;
+  enqueueTask([=]() {
+    auto MBOrErr = Future->get();
+    if (MBOrErr.second)
+      fatal(MBOrErr.second, "could not open " + PathStr);
+    Driver->addBuffer(std::move(MBOrErr.first));
+  });
+
   if (Config->OutputFile == "")
-    Config->OutputFile = getOutputPath(MB.getBufferIdentifier());
-  return std::unique_ptr<InputFile>(new ObjectFile(MB));
+    Config->OutputFile = getOutputPath(Path);
+}
+
+void LinkerDriver::addArchiveBuffer(MemoryBufferRef MB, StringRef SymName,
+                                    StringRef ParentName) {
+  file_magic Magic = identify_magic(MB.getBuffer());
+  if (Magic == file_magic::coff_import_library) {
+    Symtab.addFile(make<ImportFile>(MB));
+    return;
+  }
+
+  InputFile *Obj;
+  if (Magic == file_magic::coff_object)
+    Obj = make<ObjectFile>(MB);
+  else if (Magic == file_magic::bitcode)
+    Obj = make<BitcodeFile>(MB);
+  else
+    fatal("unknown file type: " + MB.getBufferIdentifier());
+
+  Obj->ParentName = ParentName;
+  Symtab.addFile(Obj);
+  if (Config->Verbose)
+    outs() << "Loaded " << toString(Obj) << " for " << SymName << "\n";
+}
+
+void LinkerDriver::enqueueArchiveMember(const Archive::Child &C,
+                                        StringRef SymName,
+                                        StringRef ParentName) {
+  if (!C.getParent()->isThin()) {
+    MemoryBufferRef MB = check(
+        C.getMemoryBufferRef(),
+        "could not get the buffer for the member defining symbol " + SymName);
+    enqueueTask([=]() { Driver->addArchiveBuffer(MB, SymName, ParentName); });
+    return;
+  }
+
+  auto Future = std::make_shared<std::future<MBErrPair>>(createFutureForFile(
+      check(C.getFullName(),
+            "could not get the filename for the member defining symbol " +
+                SymName)));
+  enqueueTask([=]() {
+    auto MBOrErr = Future->get();
+    if (MBOrErr.second)
+      fatal(MBOrErr.second,
+            "could not get the buffer for the member defining " + SymName);
+    Driver->addArchiveBuffer(takeBuffer(std::move(MBOrErr.first)), SymName,
+                             ParentName);
+  });
 }
 
 static bool isDecorated(StringRef Sym) {
@@ -87,7 +195,7 @@ static bool isDecorated(StringRef Sym) {
 // Parses .drectve section contents and returns a list of files
 // specified by /defaultlib.
 void LinkerDriver::parseDirectives(StringRef S) {
-  llvm::opt::InputArgList Args = Parser.parse(S);
+  opt::InputArgList Args = Parser.parse(S);
 
   for (auto *Arg : Args) {
     switch (Arg->getOption().getID()) {
@@ -95,10 +203,8 @@ void LinkerDriver::parseDirectives(StringRef S) {
       parseAlternateName(Arg->getValue());
       break;
     case OPT_defaultlib:
-      if (Optional<StringRef> Path = findLib(Arg->getValue())) {
-        MemoryBufferRef MB = openFile(*Path);
-        Symtab.addFile(createFile(MB));
-      }
+      if (Optional<StringRef> Path = findLib(Arg->getValue()))
+        enqueuePath(*Path);
       break;
     case OPT_export: {
       Export E = parseExport(Arg->getValue());
@@ -135,19 +241,19 @@ void LinkerDriver::parseDirectives(StringRef S) {
 // Find file from search paths. You can omit ".obj", this function takes
 // care of that. Note that the returned path is not guaranteed to exist.
 StringRef LinkerDriver::doFindFile(StringRef Filename) {
-  bool hasPathSep = (Filename.find_first_of("/\\") != StringRef::npos);
-  if (hasPathSep)
+  bool HasPathSep = (Filename.find_first_of("/\\") != StringRef::npos);
+  if (HasPathSep)
     return Filename;
-  bool hasExt = (Filename.find('.') != StringRef::npos);
+  bool HasExt = (Filename.find('.') != StringRef::npos);
   for (StringRef Dir : SearchPaths) {
     SmallString<128> Path = Dir;
-    llvm::sys::path::append(Path, Filename);
-    if (llvm::sys::fs::exists(Path.str()))
-      return Alloc.save(Path.str());
-    if (!hasExt) {
+    sys::path::append(Path, Filename);
+    if (sys::fs::exists(Path.str()))
+      return Saver.save(Path.str());
+    if (!HasExt) {
       Path.append(".obj");
-      if (llvm::sys::fs::exists(Path.str()))
-        return Alloc.save(Path.str());
+      if (sys::fs::exists(Path.str()))
+        return Saver.save(Path.str());
     }
   }
   return Filename;
@@ -166,9 +272,9 @@ Optional<StringRef> LinkerDriver::findFile(StringRef Filename) {
 // Find library file from search path.
 StringRef LinkerDriver::doFindLib(StringRef Filename) {
   // Add ".lib" to Filename if that has no file extension.
-  bool hasExt = (Filename.find('.') != StringRef::npos);
-  if (!hasExt)
-    Filename = Alloc.save(Filename + ".lib");
+  bool HasExt = (Filename.find('.') != StringRef::npos);
+  if (!HasExt)
+    Filename = Saver.save(Filename + ".lib");
   return doFindFile(Filename);
 }
 
@@ -178,11 +284,12 @@ StringRef LinkerDriver::doFindLib(StringRef Filename) {
 Optional<StringRef> LinkerDriver::findLib(StringRef Filename) {
   if (Config->NoDefaultLibAll)
     return None;
+  if (!VisitedLibs.insert(Filename.lower()).second)
+    return None;
   StringRef Path = doFindLib(Filename);
   if (Config->NoDefaultLibs.count(Path))
     return None;
-  bool Seen = !VisitedFiles.insert(Path.lower()).second;
-  if (Seen)
+  if (!VisitedFiles.insert(Path.lower()).second)
     return None;
   return Path;
 }
@@ -192,7 +299,7 @@ void LinkerDriver::addLibSearchPaths() {
   Optional<std::string> EnvOpt = Process::GetEnv("LIB");
   if (!EnvOpt.hasValue())
     return;
-  StringRef Env = Alloc.save(*EnvOpt);
+  StringRef Env = Saver.save(*EnvOpt);
   while (!Env.empty()) {
     StringRef Path;
     std::tie(Path, Env) = Env.split(';');
@@ -200,17 +307,17 @@ void LinkerDriver::addLibSearchPaths() {
   }
 }
 
-Undefined *LinkerDriver::addUndefined(StringRef Name) {
-  Undefined *U = Symtab.addUndefined(Name);
-  Config->GCRoot.insert(U);
-  return U;
+SymbolBody *LinkerDriver::addUndefined(StringRef Name) {
+  SymbolBody *B = Symtab.addUndefined(Name);
+  Config->GCRoot.insert(B);
+  return B;
 }
 
 // Symbol names are mangled by appending "_" prefix on x86.
 StringRef LinkerDriver::mangle(StringRef Sym) {
   assert(Config->Machine != IMAGE_FILE_MACHINE_UNKNOWN);
   if (Config->Machine == I386)
-    return Alloc.save("_" + Sym);
+    return Saver.save("_" + Sym);
   return Sym;
 }
 
@@ -225,7 +332,7 @@ StringRef LinkerDriver::findDefaultEntry() {
   };
   for (auto E : Entries) {
     StringRef Entry = Symtab.findMangle(mangle(E[0]));
-    if (!Entry.empty() && !isa<Undefined>(Symtab.find(Entry)->Body))
+    if (!Entry.empty() && !isa<Undefined>(Symtab.find(Entry)->body()))
       return mangle(E[1]);
   }
   return "";
@@ -247,7 +354,83 @@ static uint64_t getDefaultImageBase() {
   return Config->DLL ? 0x10000000 : 0x400000;
 }
 
-void LinkerDriver::link(llvm::ArrayRef<const char *> ArgsArr) {
+static std::string createResponseFile(const opt::InputArgList &Args,
+                                      ArrayRef<StringRef> FilePaths,
+                                      ArrayRef<StringRef> SearchPaths) {
+  SmallString<0> Data;
+  raw_svector_ostream OS(Data);
+
+  for (auto *Arg : Args) {
+    switch (Arg->getOption().getID()) {
+    case OPT_linkrepro:
+    case OPT_INPUT:
+    case OPT_defaultlib:
+    case OPT_libpath:
+      break;
+    default:
+      OS << stringize(Arg) << "\n";
+    }
+  }
+
+  for (StringRef Path : SearchPaths) {
+    std::string RelPath = relativeToRoot(Path);
+    OS << "/libpath:" << quote(RelPath) << "\n";
+  }
+
+  for (StringRef Path : FilePaths)
+    OS << quote(relativeToRoot(Path)) << "\n";
+
+  return Data.str();
+}
+
+static unsigned getDefaultDebugType(const opt::InputArgList &Args) {
+  unsigned DebugTypes = static_cast<unsigned>(DebugType::CV);
+  if (Args.hasArg(OPT_driver))
+    DebugTypes |= static_cast<unsigned>(DebugType::PData);
+  if (Args.hasArg(OPT_profile))
+    DebugTypes |= static_cast<unsigned>(DebugType::Fixup);
+  return DebugTypes;
+}
+
+static unsigned parseDebugType(StringRef Arg) {
+  SmallVector<StringRef, 3> Types;
+  Arg.split(Types, ',', /*KeepEmpty=*/false);
+
+  unsigned DebugTypes = static_cast<unsigned>(DebugType::None);
+  for (StringRef Type : Types)
+    DebugTypes |= StringSwitch<unsigned>(Type.lower())
+                      .Case("cv", static_cast<unsigned>(DebugType::CV))
+                      .Case("pdata", static_cast<unsigned>(DebugType::PData))
+                      .Case("fixup", static_cast<unsigned>(DebugType::Fixup));
+  return DebugTypes;
+}
+
+static std::string getMapFile(const opt::InputArgList &Args) {
+  auto *Arg = Args.getLastArg(OPT_lldmap, OPT_lldmap_file);
+  if (!Arg)
+    return "";
+  if (Arg->getOption().getID() == OPT_lldmap_file)
+    return Arg->getValue();
+
+  assert(Arg->getOption().getID() == OPT_lldmap);
+  StringRef OutFile = Config->OutputFile;
+  return (OutFile.substr(0, OutFile.rfind('.')) + ".map").str();
+}
+
+void LinkerDriver::enqueueTask(std::function<void()> Task) {
+  TaskQueue.push_back(std::move(Task));
+}
+
+bool LinkerDriver::run() {
+  bool DidWork = !TaskQueue.empty();
+  while (!TaskQueue.empty()) {
+    TaskQueue.front()();
+    TaskQueue.pop_front();
+  }
+  return DidWork;
+}
+
+void LinkerDriver::link(ArrayRef<const char *> ArgsArr) {
   // If the first command line argument is "/lib", link.exe acts like lib.exe.
   // We call our own implementation of lib.exe that understands bitcode files.
   if (ArgsArr.size() > 1 && StringRef(ArgsArr[1]).equals_lower("/lib")) {
@@ -257,15 +440,15 @@ void LinkerDriver::link(llvm::ArrayRef<const char *> ArgsArr) {
   }
 
   // Needed for LTO.
-  llvm::InitializeAllTargetInfos();
-  llvm::InitializeAllTargets();
-  llvm::InitializeAllTargetMCs();
-  llvm::InitializeAllAsmParsers();
-  llvm::InitializeAllAsmPrinters();
-  llvm::InitializeAllDisassemblers();
+  InitializeAllTargetInfos();
+  InitializeAllTargets();
+  InitializeAllTargetMCs();
+  InitializeAllAsmParsers();
+  InitializeAllAsmPrinters();
+  InitializeAllDisassemblers();
 
   // Parse command line options.
-  llvm::opt::InputArgList Args = Parser.parseLINK(ArgsArr.slice(1));
+  opt::InputArgList Args = Parser.parseLINK(ArgsArr.slice(1));
 
   // Handle /help
   if (Args.hasArg(OPT_help)) {
@@ -273,6 +456,17 @@ void LinkerDriver::link(llvm::ArrayRef<const char *> ArgsArr) {
     return;
   }
 
+  if (auto *Arg = Args.getLastArg(OPT_linkrepro)) {
+    SmallString<64> Path = StringRef(Arg->getValue());
+    sys::path::append(Path, "repro");
+    ErrorOr<CpioFile *> F = CpioFile::create(Path);
+    if (F)
+      Cpio.reset(*F);
+    else
+      errs() << "/linkrepro: failed to open " << Path
+             << ".cpio: " << F.getError().message() << '\n';
+  }
+
   if (Args.filtered_begin(OPT_INPUT) == Args.filtered_end())
     fatal("no input files");
 
@@ -295,8 +489,17 @@ void LinkerDriver::link(llvm::ArrayRef<const char *> ArgsArr) {
     Config->Force = true;
 
   // Handle /debug
-  if (Args.hasArg(OPT_debug))
+  if (Args.hasArg(OPT_debug)) {
     Config->Debug = true;
+    Config->DebugTypes =
+        Args.hasArg(OPT_debugtype)
+            ? parseDebugType(Args.getLastArg(OPT_debugtype)->getValue())
+            : getDefaultDebugType(Args);
+  }
+
+  // Create a dummy PDB file to satisfy build sytem rules.
+  if (auto *Arg = Args.getLastArg(OPT_pdb))
+    Config->PDBPath = Arg->getValue();
 
   // Handle /noentry
   if (Args.hasArg(OPT_noentry)) {
@@ -447,72 +650,43 @@ void LinkerDriver::link(llvm::ArrayRef<const char *> ArgsArr) {
     Config->TerminalServerAware = false;
   if (Args.hasArg(OPT_nosymtab))
     Config->WriteSymtab = false;
+  Config->DumpPdb = Args.hasArg(OPT_dumppdb);
+  Config->DebugPdb = Args.hasArg(OPT_debugpdb);
 
   // Create a list of input files. Files can be given as arguments
   // for /defaultlib option.
-  std::vector<StringRef> Paths;
   std::vector<MemoryBufferRef> MBs;
   for (auto *Arg : Args.filtered(OPT_INPUT))
     if (Optional<StringRef> Path = findFile(Arg->getValue()))
-      Paths.push_back(*Path);
+      enqueuePath(*Path);
   for (auto *Arg : Args.filtered(OPT_defaultlib))
     if (Optional<StringRef> Path = findLib(Arg->getValue()))
-      Paths.push_back(*Path);
-  for (StringRef Path : Paths)
-    MBs.push_back(openFile(Path));
+      enqueuePath(*Path);
 
   // Windows specific -- Create a resource file containing a manifest file.
-  if (Config->Manifest == Configuration::Embed) {
-    std::unique_ptr<MemoryBuffer> MB = createManifestRes();
-    MBs.push_back(MB->getMemBufferRef());
-    OwningMBs.push_back(std::move(MB)); // take ownership
-  }
+  if (Config->Manifest == Configuration::Embed)
+    addBuffer(createManifestRes());
 
-  // Windows specific -- Input files can be Windows resource files (.res files).
-  // We invoke cvtres.exe to convert resource files to a regular COFF file
-  // then link the result file normally.
-  std::vector<MemoryBufferRef> Resources;
-  auto NotResource = [](MemoryBufferRef MB) {
-    return identify_magic(MB.getBuffer()) != file_magic::windows_resource;
-  };
-  auto It = std::stable_partition(MBs.begin(), MBs.end(), NotResource);
-  if (It != MBs.end()) {
-    Resources.insert(Resources.end(), It, MBs.end());
-    MBs.erase(It, MBs.end());
-  }
+  // Read all input files given via the command line.
+  run();
 
-  // Read all input files given via the command line. Note that step()
-  // doesn't read files that are specified by directive sections.
-  for (MemoryBufferRef MB : MBs)
-    Symtab.addFile(createFile(MB));
-  Symtab.step();
-
-  // Determine machine type and check if all object files are
-  // for the same CPU type. Note that this needs to be done before
-  // any call to mangle().
-  for (std::unique_ptr<InputFile> &File : Symtab.getFiles()) {
-    MachineTypes MT = File->getMachineType();
-    if (MT == IMAGE_FILE_MACHINE_UNKNOWN)
-      continue;
-    if (Config->Machine == IMAGE_FILE_MACHINE_UNKNOWN) {
-      Config->Machine = MT;
-      continue;
-    }
-    if (Config->Machine != MT)
-      fatal(File->getShortName() + ": machine type " + machineToStr(MT) +
-            " conflicts with " + machineToStr(Config->Machine));
-  }
+  // We should have inferred a machine type by now from the input files, but if
+  // not we assume x64.
   if (Config->Machine == IMAGE_FILE_MACHINE_UNKNOWN) {
-    llvm::errs() << "warning: /machine is not specified. x64 is assumed.\n";
+    errs() << "warning: /machine is not specified. x64 is assumed.\n";
     Config->Machine = AMD64;
   }
 
-  // Windows specific -- Convert Windows resource files to a COFF file.
-  if (!Resources.empty()) {
-    std::unique_ptr<MemoryBuffer> MB = convertResToCOFF(Resources);
-    Symtab.addFile(createFile(MB->getMemBufferRef()));
-    OwningMBs.push_back(std::move(MB)); // take ownership
-  }
+  // Windows specific -- Input files can be Windows resource files (.res files).
+  // We invoke cvtres.exe to convert resource files to a regular COFF file
+  // then link the result file normally.
+  if (!Resources.empty())
+    addBuffer(convertResToCOFF(Resources));
+
+  if (Cpio)
+    Cpio->append("response.txt",
+                 createResponseFile(Args, FilePaths,
+                                    ArrayRef<StringRef>(SearchPaths).slice(1)));
 
   // Handle /largeaddressaware
   if (Config->is64() || Args.hasArg(OPT_largeaddressaware))
@@ -537,7 +711,7 @@ void LinkerDriver::link(llvm::ArrayRef<const char *> ArgsArr) {
       fatal("entry point must be defined");
     Config->Entry = addUndefined(S);
     if (Config->Verbose)
-      llvm::outs() << "Entry name inferred: " << S << "\n";
+      outs() << "Entry name inferred: " << S << "\n";
   }
 
   // Handle /export
@@ -545,18 +719,19 @@ void LinkerDriver::link(llvm::ArrayRef<const char *> ArgsArr) {
     Export E = parseExport(Arg->getValue());
     if (Config->Machine == I386) {
       if (!isDecorated(E.Name))
-        E.Name = Alloc.save("_" + E.Name);
+        E.Name = Saver.save("_" + E.Name);
       if (!E.ExtName.empty() && !isDecorated(E.ExtName))
-        E.ExtName = Alloc.save("_" + E.ExtName);
+        E.ExtName = Saver.save("_" + E.ExtName);
     }
     Config->Exports.push_back(E);
   }
 
   // Handle /def
   if (auto *Arg = Args.getLastArg(OPT_deffile)) {
-    MemoryBufferRef MB = openFile(Arg->getValue());
     // parseModuleDefs mutates Config object.
-    parseModuleDefs(MB, &Alloc);
+    parseModuleDefs(
+        takeBuffer(check(MemoryBuffer::getFile(Arg->getValue()),
+                         Twine("could not open ") + Arg->getValue())));
   }
 
   // Handle /delayload
@@ -585,14 +760,10 @@ void LinkerDriver::link(llvm::ArrayRef<const char *> ArgsArr) {
   Symtab.addAbsolute(mangle("__guard_fids_count"), 0);
   Symtab.addAbsolute(mangle("__guard_flags"), 0x100);
 
-  // Read as much files as we can from directives sections.
-  Symtab.run();
-
-  // Resolve auxiliary symbols until we get a convergence.
-  // (Trying to resolve a symbol may trigger a Lazy symbol to load a new file.
-  // A new file may contain a directive section to add new command line options.
-  // That's why we have to repeat until converge.)
-  for (;;) {
+  // This code may add new undefined symbols to the link, which may enqueue more
+  // symbol resolution tasks, so we need to continue executing tasks until we
+  // converge.
+  do {
     // Windows specific -- if entry point is not found,
     // search for its mangled names.
     if (Config->Entry)
@@ -615,7 +786,7 @@ void LinkerDriver::link(llvm::ArrayRef<const char *> ArgsArr) {
       Symbol *Sym = Symtab.find(From);
       if (!Sym)
         continue;
-      if (auto *U = dyn_cast<Undefined>(Sym->Body))
+      if (auto *U = dyn_cast<Undefined>(Sym->body()))
         if (!U->WeakAlias)
           U->WeakAlias = Symtab.addUndefined(To);
     }
@@ -623,18 +794,15 @@ void LinkerDriver::link(llvm::ArrayRef<const char *> ArgsArr) {
     // Windows specific -- if __load_config_used can be resolved, resolve it.
     if (Symtab.findUnderscore("_load_config_used"))
       addUndefined(mangle("_load_config_used"));
-
-    if (Symtab.queueEmpty())
-      break;
-    Symtab.run();
-  }
+  } while (run());
 
   // Do LTO by compiling bitcode input files to a set of native COFF files then
   // link those files.
   Symtab.addCombinedLTOObjects();
+  run();
 
   // Make sure we have resolved all symbols.
-  Symtab.reportRemainingUndefines(/*Resolve=*/true);
+  Symtab.reportRemainingUndefines();
 
   // Windows specific -- if no /subsystem is given, we need to infer
   // that from entry point name.
@@ -662,10 +830,6 @@ void LinkerDriver::link(llvm::ArrayRef<const char *> ArgsArr) {
   if (Config->Manifest == Configuration::SideBySide)
     createSideBySideManifest();
 
-  // Create a dummy PDB file to satisfy build sytem rules.
-  if (auto *Arg = Args.getLastArg(OPT_pdb))
-    createPDB(Arg->getValue());
-
   // Identify unreferenced COMDAT sections.
   if (Config->DoGC)
     markLive(Symtab.getChunks());
@@ -679,13 +843,15 @@ void LinkerDriver::link(llvm::ArrayRef<const char *> ArgsArr) {
 
   // Create a symbol map file containing symbol VAs and their names
   // to help debugging.
-  if (auto *Arg = Args.getLastArg(OPT_lldmap)) {
+  std::string MapFile = getMapFile(Args);
+  if (!MapFile.empty()) {
     std::error_code EC;
-    llvm::raw_fd_ostream Out(Arg->getValue(), EC, OpenFlags::F_Text);
+    raw_fd_ostream Out(MapFile, EC, OpenFlags::F_Text);
     if (EC)
-      fatal(EC, "could not create the symbol map");
+      fatal(EC, "could not create the symbol map " + MapFile);
     Symtab.printMap(Out);
   }
+
   // Call exit to avoid calling destructors.
   exit(0);
 }
diff --git a/COFF/Driver.h b/COFF/Driver.h
index 23969ee802fb..e8114640edec 100644
--- a/COFF/Driver.h
+++ b/COFF/Driver.h
@@ -13,12 +13,13 @@
 #include "Config.h"
 #include "SymbolTable.h"
 #include "lld/Core/LLVM.h"
+#include "lld/Core/Reproduce.h"
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/StringRef.h"
+#include "llvm/Object/Archive.h"
 #include "llvm/Object/COFF.h"
 #include "llvm/Option/Arg.h"
 #include "llvm/Option/ArgList.h"
-#include "llvm/Support/StringSaver.h"
 #include <memory>
 #include <set>
 #include <vector>
@@ -42,7 +43,6 @@ void doICF(const std::vector<Chunk *> &Chunks);
 
 class ArgParser {
 public:
-  ArgParser() : Alloc(AllocAux) {}
   // Parses command line options.
   llvm::opt::InputArgList parse(llvm::ArrayRef<const char *> Args);
 
@@ -56,25 +56,26 @@ private:
   std::vector<const char *> tokenize(StringRef S);
 
   std::vector<const char *> replaceResponseFiles(std::vector<const char *>);
-
-  llvm::BumpPtrAllocator AllocAux;
-  llvm::StringSaver Alloc;
 };
 
 class LinkerDriver {
 public:
-  LinkerDriver() : Alloc(AllocAux) {}
+  LinkerDriver() { coff::Symtab = &Symtab; }
   void link(llvm::ArrayRef<const char *> Args);
 
   // Used by the resolver to parse .drectve section contents.
   void parseDirectives(StringRef S);
 
+  // Used by ArchiveFile to enqueue members.
+  void enqueueArchiveMember(const Archive::Child &C, StringRef SymName,
+                            StringRef ParentName);
+
 private:
-  llvm::BumpPtrAllocator AllocAux;
-  llvm::StringSaver Alloc;
   ArgParser Parser;
   SymbolTable Symtab;
 
+  std::unique_ptr<CpioFile> Cpio; // for /linkrepro
+
   // Opens a file. Path has to be resolved already.
   MemoryBufferRef openFile(StringRef Path);
 
@@ -90,8 +91,9 @@ private:
   // Library search path. The first element is always "" (current directory).
   std::vector<StringRef> SearchPaths;
   std::set<std::string> VisitedFiles;
+  std::set<std::string> VisitedLibs;
 
-  Undefined *addUndefined(StringRef Sym);
+  SymbolBody *addUndefined(StringRef Sym);
   StringRef mangle(StringRef Sym);
 
   // Windows specific -- "main" is not the only main function in Windows.
@@ -104,12 +106,26 @@ private:
   StringRef findDefaultEntry();
   WindowsSubsystem inferSubsystem();
 
+  MemoryBufferRef takeBuffer(std::unique_ptr<MemoryBuffer> MB);
+  void addBuffer(std::unique_ptr<MemoryBuffer> MB);
+  void addArchiveBuffer(MemoryBufferRef MBRef, StringRef SymName,
+                        StringRef ParentName);
+
+  void enqueuePath(StringRef Path);
+
+  void enqueueTask(std::function<void()> Task);
+  bool run();
+
   // Driver is the owner of all opened files.
   // InputFiles have MemoryBufferRefs to them.
   std::vector<std::unique_ptr<MemoryBuffer>> OwningMBs;
+
+  std::list<std::function<void()>> TaskQueue;
+  std::vector<StringRef> FilePaths;
+  std::vector<MemoryBufferRef> Resources;
 };
 
-void parseModuleDefs(MemoryBufferRef MB, llvm::StringSaver *Alloc);
+void parseModuleDefs(MemoryBufferRef MB);
 void writeImportLibrary();
 
 // Functions below this line are defined in DriverUtils.cpp.
@@ -161,8 +177,6 @@ void checkFailIfMismatch(StringRef Arg);
 std::unique_ptr<MemoryBuffer>
 convertResToCOFF(const std::vector<MemoryBufferRef> &MBs);
 
-void createPDB(StringRef Path);
-
 // Create enum with OPT_xxx values for each option in Options.td
 enum {
   OPT_INVALID = 0,
diff --git a/COFF/DriverUtils.cpp b/COFF/DriverUtils.cpp
index 5d7dc2bc65af..14dd004f1c04 100644
--- a/COFF/DriverUtils.cpp
+++ b/COFF/DriverUtils.cpp
@@ -16,6 +16,7 @@
 #include "Config.h"
 #include "Driver.h"
 #include "Error.h"
+#include "Memory.h"
 #include "Symbols.h"
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/StringSwitch.h"
@@ -43,29 +44,29 @@ namespace {
 class Executor {
 public:
   explicit Executor(StringRef S) : Saver(Alloc), Prog(Saver.save(S)) {}
-  void add(StringRef S)    { Args.push_back(Saver.save(S)); }
-  void add(std::string &S) { Args.push_back(Saver.save(S)); }
-  void add(Twine S)        { Args.push_back(Saver.save(S)); }
-  void add(const char *S)  { Args.push_back(Saver.save(S)); }
+  void add(StringRef S) { Args.push_back(Saver.save(S).data()); }
+  void add(std::string &S) { Args.push_back(Saver.save(S).data()); }
+  void add(Twine S) { Args.push_back(Saver.save(S).data()); }
+  void add(const char *S) { Args.push_back(Saver.save(S).data()); }
 
   void run() {
-    ErrorOr<std::string> ExeOrErr = llvm::sys::findProgramByName(Prog);
+    ErrorOr<std::string> ExeOrErr = sys::findProgramByName(Prog);
     if (auto EC = ExeOrErr.getError())
       fatal(EC, "unable to find " + Prog + " in PATH: ");
-    const char *Exe = Saver.save(*ExeOrErr);
+    const char *Exe = Saver.save(*ExeOrErr).data();
     Args.insert(Args.begin(), Exe);
     Args.push_back(nullptr);
-    if (llvm::sys::ExecuteAndWait(Args[0], Args.data()) != 0) {
+    if (sys::ExecuteAndWait(Args[0], Args.data()) != 0) {
       for (const char *S : Args)
         if (S)
-          llvm::errs() << S << " ";
+          errs() << S << " ";
       fatal("ExecuteAndWait failed");
     }
   }
 
 private:
-  llvm::BumpPtrAllocator Alloc;
-  llvm::StringSaver Saver;
+  BumpPtrAllocator Alloc;
+  StringSaver Saver;
   StringRef Prog;
   std::vector<const char *> Args;
 };
@@ -75,10 +76,8 @@ private:
 // Returns /machine's value.
 MachineTypes getMachineType(StringRef S) {
   MachineTypes MT = StringSwitch<MachineTypes>(S.lower())
-                        .Case("x64", AMD64)
-                        .Case("amd64", AMD64)
-                        .Case("x86", I386)
-                        .Case("i386", I386)
+                        .Cases("x64", "amd64", AMD64)
+                        .Cases("x86", "i386", I386)
                         .Case("arm", ARMNT)
                         .Default(IMAGE_FILE_MACHINE_UNKNOWN);
   if (MT != IMAGE_FILE_MACHINE_UNKNOWN)
@@ -168,8 +167,8 @@ void parseMerge(StringRef S) {
   if (!Inserted) {
     StringRef Existing = Pair.first->second;
     if (Existing != To)
-      llvm::errs() << "warning: " << S << ": already merged into "
-                   << Existing << "\n";
+      errs() << "warning: " << S << ": already merged into " << Existing
+             << "\n";
   }
 }
 
@@ -279,18 +278,54 @@ static void quoteAndPrint(raw_ostream &Out, StringRef S) {
   }
 }
 
+// An RAII temporary file class that automatically removes a temporary file.
+namespace {
+class TemporaryFile {
+public:
+  TemporaryFile(StringRef Prefix, StringRef Extn) {
+    SmallString<128> S;
+    if (auto EC = sys::fs::createTemporaryFile("lld-" + Prefix, Extn, S))
+      fatal(EC, "cannot create a temporary file");
+    Path = S.str();
+  }
+
+  TemporaryFile(TemporaryFile &&Obj) {
+    std::swap(Path, Obj.Path);
+  }
+
+  ~TemporaryFile() {
+    if (Path.empty())
+      return;
+    if (sys::fs::remove(Path))
+      fatal("failed to remove " + Path);
+  }
+
+  // Returns a memory buffer of this temporary file.
+  // Note that this function does not leave the file open,
+  // so it is safe to remove the file immediately after this function
+  // is called (you cannot remove an opened file on Windows.)
+  std::unique_ptr<MemoryBuffer> getMemoryBuffer() {
+    // IsVolatileSize=true forces MemoryBuffer to not use mmap().
+    return check(MemoryBuffer::getFile(Path, /*FileSize=*/-1,
+                                       /*RequiresNullTerminator=*/false,
+                                       /*IsVolatileSize=*/true),
+                 "could not open " + Path);
+  }
+
+  std::string Path;
+};
+}
+
 // Create the default manifest file as a temporary file.
-static std::string createDefaultXml() {
+TemporaryFile createDefaultXml() {
   // Create a temporary file.
-  SmallString<128> Path;
-  if (auto EC = sys::fs::createTemporaryFile("tmp", "manifest", Path))
-    fatal(EC, "cannot create a temporary file");
+  TemporaryFile File("defaultxml", "manifest");
 
   // Open the temporary file for writing.
   std::error_code EC;
-  llvm::raw_fd_ostream OS(Path, EC, sys::fs::F_Text);
+  raw_fd_ostream OS(File.Path, EC, sys::fs::F_Text);
   if (EC)
-    fatal(EC, "failed to open " + Path);
+    fatal(EC, "failed to open " + File.Path);
 
   // Emit the XML. Note that we do *not* verify that the XML attributes are
   // syntactically correct. This is intentional for link.exe compatibility.
@@ -316,56 +351,48 @@ static std::string createDefaultXml() {
   }
   OS << "</assembly>\n";
   OS.close();
-  return StringRef(Path);
+  return File;
 }
 
 static std::string readFile(StringRef Path) {
   std::unique_ptr<MemoryBuffer> MB =
       check(MemoryBuffer::getFile(Path), "could not open " + Path);
-  std::unique_ptr<MemoryBuffer> Buf(std::move(MB));
-  return Buf->getBuffer();
+  return MB->getBuffer();
 }
 
 static std::string createManifestXml() {
   // Create the default manifest file.
-  std::string Path1 = createDefaultXml();
+  TemporaryFile File1 = createDefaultXml();
   if (Config->ManifestInput.empty())
-    return readFile(Path1);
+    return readFile(File1.Path);
 
   // If manifest files are supplied by the user using /MANIFESTINPUT
   // option, we need to merge them with the default manifest.
-  SmallString<128> Path2;
-  if (auto EC = sys::fs::createTemporaryFile("tmp", "manifest", Path2))
-    fatal(EC, "cannot create a temporary file");
-  FileRemover Remover1(Path1);
-  FileRemover Remover2(Path2);
+  TemporaryFile File2("user", "manifest");
 
   Executor E("mt.exe");
   E.add("/manifest");
-  E.add(Path1);
+  E.add(File1.Path);
   for (StringRef Filename : Config->ManifestInput) {
     E.add("/manifest");
     E.add(Filename);
   }
   E.add("/nologo");
-  E.add("/out:" + StringRef(Path2));
+  E.add("/out:" + StringRef(File2.Path));
   E.run();
-  return readFile(Path2);
+  return readFile(File2.Path);
 }
 
 // Create a resource file containing a manifest XML.
 std::unique_ptr<MemoryBuffer> createManifestRes() {
   // Create a temporary file for the resource script file.
-  SmallString<128> RCPath;
-  if (auto EC = sys::fs::createTemporaryFile("tmp", "rc", RCPath))
-    fatal(EC, "cannot create a temporary file");
-  FileRemover RCRemover(RCPath);
+  TemporaryFile RCFile("manifest", "rc");
 
   // Open the temporary file for writing.
   std::error_code EC;
-  llvm::raw_fd_ostream Out(RCPath, EC, sys::fs::F_Text);
+  raw_fd_ostream Out(RCFile.Path, EC, sys::fs::F_Text);
   if (EC)
-    fatal(EC, "failed to open " + RCPath);
+    fatal(EC, "failed to open " + RCFile.Path);
 
   // Write resource script to the RC file.
   Out << "#define LANG_ENGLISH 9\n"
@@ -379,17 +406,15 @@ std::unique_ptr<MemoryBuffer> createManifestRes() {
   Out.close();
 
   // Create output resource file.
-  SmallString<128> ResPath;
-  if (auto EC = sys::fs::createTemporaryFile("tmp", "res", ResPath))
-    fatal(EC, "cannot create a temporary file");
+  TemporaryFile ResFile("output-resource", "res");
 
   Executor E("rc.exe");
   E.add("/fo");
-  E.add(ResPath.str());
+  E.add(ResFile.Path);
   E.add("/nologo");
-  E.add(RCPath.str());
+  E.add(RCFile.Path);
   E.run();
-  return check(MemoryBuffer::getFile(ResPath), "could not open " + ResPath);
+  return ResFile.getMemoryBuffer();
 }
 
 void createSideBySideManifest() {
@@ -397,7 +422,7 @@ void createSideBySideManifest() {
   if (Path == "")
     Path = Config->OutputFile + ".manifest";
   std::error_code EC;
-  llvm::raw_fd_ostream Out(Path, EC, llvm::sys::fs::F_Text);
+  raw_fd_ostream Out(Path, EC, sys::fs::F_Text);
   if (EC)
     fatal(EC, "failed to create manifest");
   Out << createManifestXml();
@@ -485,12 +510,14 @@ void fixupExports() {
   }
 
   for (Export &E : Config->Exports) {
+    SymbolBody *Sym = E.Sym;
     if (!E.ForwardTo.empty()) {
       E.SymbolName = E.Name;
-    } else if (Undefined *U = cast_or_null<Undefined>(E.Sym->WeakAlias)) {
-      E.SymbolName = U->getName();
     } else {
-      E.SymbolName = E.Sym->getName();
+      if (auto *U = dyn_cast<Undefined>(Sym))
+        if (U->WeakAlias)
+          Sym = U->WeakAlias;
+      E.SymbolName = Sym->getName();
     }
   }
 
@@ -515,7 +542,7 @@ void fixupExports() {
     Export *Existing = Pair.first->second;
     if (E == *Existing || E.Name != Existing->Name)
       continue;
-    llvm::errs() << "warning: duplicate /export option: " << E.Name << "\n";
+    errs() << "warning: duplicate /export option: " << E.Name << "\n";
   }
   Config->Exports = std::move(V);
 
@@ -555,20 +582,39 @@ void checkFailIfMismatch(StringRef Arg) {
 std::unique_ptr<MemoryBuffer>
 convertResToCOFF(const std::vector<MemoryBufferRef> &MBs) {
   // Create an output file path.
-  SmallString<128> Path;
-  if (auto EC = llvm::sys::fs::createTemporaryFile("resource", "obj", Path))
-    fatal(EC, "could not create temporary file");
+  TemporaryFile File("resource-file", "obj");
 
   // Execute cvtres.exe.
   Executor E("cvtres.exe");
   E.add("/machine:" + machineToStr(Config->Machine));
   E.add("/readonly");
   E.add("/nologo");
-  E.add("/out:" + Path);
-  for (MemoryBufferRef MB : MBs)
-    E.add(MB.getBufferIdentifier());
+  E.add("/out:" + Twine(File.Path));
+
+  // We must create new files because the memory buffers we have may have no
+  // underlying file still existing on the disk.
+  // It happens if it was created from a TemporaryFile, which usually delete
+  // the file just after creating the MemoryBuffer.
+  std::vector<TemporaryFile> ResFiles;
+  ResFiles.reserve(MBs.size());
+  for (MemoryBufferRef MB : MBs) {
+    // We store the temporary file in a vector to avoid deletion
+    // before running cvtres
+    ResFiles.emplace_back("resource-file", "res");
+    TemporaryFile& ResFile = ResFiles.back();
+    // Write the content of the resource in a temporary file
+    std::error_code EC;
+    raw_fd_ostream OS(ResFile.Path, EC, sys::fs::F_None);
+    if (EC)
+      fatal(EC, "failed to open " + ResFile.Path);
+    OS << MB.getBuffer();
+    OS.close();
+
+    E.add(ResFile.Path);
+  }
+
   E.run();
-  return check(MemoryBuffer::getFile(Path), "could not open " + Path);
+  return File.getMemoryBuffer();
 }
 
 // Create OptTable
@@ -595,7 +641,7 @@ public:
 };
 
 // Parses a given list of options.
-llvm::opt::InputArgList ArgParser::parse(ArrayRef<const char *> ArgsArr) {
+opt::InputArgList ArgParser::parse(ArrayRef<const char *> ArgsArr) {
   // First, replace respnose files (@<file>-style options).
   std::vector<const char *> Argv = replaceResponseFiles(ArgsArr);
 
@@ -603,28 +649,28 @@ llvm::opt::InputArgList ArgParser::parse(ArrayRef<const char *> ArgsArr) {
   COFFOptTable Table;
   unsigned MissingIndex;
   unsigned MissingCount;
-  llvm::opt::InputArgList Args =
-      Table.ParseArgs(Argv, MissingIndex, MissingCount);
+  opt::InputArgList Args = Table.ParseArgs(Argv, MissingIndex, MissingCount);
 
   // Print the real command line if response files are expanded.
   if (Args.hasArg(OPT_verbose) && ArgsArr.size() != Argv.size()) {
-    llvm::outs() << "Command line:";
+    outs() << "Command line:";
     for (const char *S : Argv)
-      llvm::outs() << " " << S;
-    llvm::outs() << "\n";
+      outs() << " " << S;
+    outs() << "\n";
   }
 
   if (MissingCount)
-    fatal("missing arg value for \"" + Twine(Args.getArgString(MissingIndex)) +
-          "\", expected " + Twine(MissingCount) +
-          (MissingCount == 1 ? " argument." : " arguments."));
+    fatal(Twine(Args.getArgString(MissingIndex)) + ": missing argument");
   for (auto *Arg : Args.filtered(OPT_UNKNOWN))
-    llvm::errs() << "ignoring unknown argument: " << Arg->getSpelling() << "\n";
+    errs() << "ignoring unknown argument: " << Arg->getSpelling() << "\n";
   return Args;
 }
 
-llvm::opt::InputArgList ArgParser::parseLINK(ArrayRef<const char *> Args) {
-  // Concatenate LINK env and given arguments and parse them.
+// link.exe has an interesting feature. If LINK environment exists,
+// its contents are handled as a command line string. So you can pass
+// extra arguments using the environment variable.
+opt::InputArgList ArgParser::parseLINK(ArrayRef<const char *> Args) {
+  // Concatenate LINK env and command line arguments, and then parse them.
   Optional<std::string> Env = Process::GetEnv("LINK");
   if (!Env)
     return parse(Args);
@@ -635,8 +681,7 @@ llvm::opt::InputArgList ArgParser::parseLINK(ArrayRef<const char *> Args) {
 
 std::vector<const char *> ArgParser::tokenize(StringRef S) {
   SmallVector<const char *, 16> Tokens;
-  StringSaver Saver(AllocAux);
-  llvm::cl::TokenizeWindowsCommandLine(S, Saver, Tokens);
+  cl::TokenizeWindowsCommandLine(S, Saver, Tokens);
   return std::vector<const char *>(Tokens.begin(), Tokens.end());
 }
 
@@ -645,14 +690,13 @@ std::vector<const char *> ArgParser::tokenize(StringRef S) {
 std::vector<const char *>
 ArgParser::replaceResponseFiles(std::vector<const char *> Argv) {
   SmallVector<const char *, 256> Tokens(Argv.data(), Argv.data() + Argv.size());
-  StringSaver Saver(AllocAux);
   ExpandResponseFiles(Saver, TokenizeWindowsCommandLine, Tokens);
   return std::vector<const char *>(Tokens.begin(), Tokens.end());
 }
 
 void printHelp(const char *Argv0) {
   COFFOptTable Table;
-  Table.PrintHelp(llvm::outs(), Argv0, "LLVM Linker", false);
+  Table.PrintHelp(outs(), Argv0, "LLVM Linker", false);
 }
 
 } // namespace coff
diff --git a/COFF/Error.cpp b/COFF/Error.cpp
index 602a8544ce2b..b2bd557413df 100644
--- a/COFF/Error.cpp
+++ b/COFF/Error.cpp
@@ -11,14 +11,31 @@
 
 #include "llvm/ADT/Twine.h"
 #include "llvm/Support/Error.h"
+#include "llvm/Support/Process.h"
 #include "llvm/Support/raw_ostream.h"
 
+#if !defined(_MSC_VER) && !defined(__MINGW32__)
+#include <unistd.h>
+#endif
+
+using namespace llvm;
+
 namespace lld {
 namespace coff {
 
 void fatal(const Twine &Msg) {
-  llvm::errs() << Msg << "\n";
-  exit(1);
+  if (sys::Process::StandardErrHasColors()) {
+    errs().changeColor(raw_ostream::RED, /*bold=*/true);
+    errs() << "error: ";
+    errs().resetColor();
+  } else {
+    errs() << "error: ";
+  }
+  errs() << Msg << "\n";
+
+  outs().flush();
+  errs().flush();
+  _exit(1);
 }
 
 void fatal(std::error_code EC, const Twine &Msg) {
diff --git a/COFF/Error.h b/COFF/Error.h
index c9f64c662580..47549327db2b 100644
--- a/COFF/Error.h
+++ b/COFF/Error.h
@@ -32,6 +32,23 @@ template <class T> T check(Expected<T> E, const Twine &Prefix) {
   return std::move(*E);
 }
 
+template <class T> T check(ErrorOr<T> EO) {
+  if (!EO)
+    fatal(EO.getError().message());
+  return std::move(*EO);
+}
+
+template <class T> T check(Expected<T> E) {
+  if (!E) {
+    std::string Buf;
+    llvm::raw_string_ostream OS(Buf);
+    logAllUnhandledErrors(E.takeError(), OS, "");
+    OS.flush();
+    fatal(Buf);
+  }
+  return std::move(*E);
+}
+
 } // namespace coff
 } // namespace lld
 
diff --git a/COFF/ICF.cpp b/COFF/ICF.cpp
index a2c5a90334d0..196fbe2610ea 100644
--- a/COFF/ICF.cpp
+++ b/COFF/ICF.cpp
@@ -7,43 +7,19 @@
 //
 //===----------------------------------------------------------------------===//
 //
-// Identical COMDAT Folding is a feature to merge COMDAT sections not by
-// name (which is regular COMDAT handling) but by contents. If two COMDAT
-// sections have the same data, relocations, attributes, etc., then the two
-// are considered identical and merged by the linker. This optimization
-// makes outputs smaller.
+// ICF is short for Identical Code Folding. That is a size optimization to
+// identify and merge two or more read-only sections (typically functions)
+// that happened to have the same contents. It usually reduces output size
+// by a few percent.
 //
-// ICF is theoretically a problem of reducing graphs by merging as many
-// identical subgraphs as possible, if we consider sections as vertices and
-// relocations as edges. This may be a bit more complicated problem than you
-// might think. The order of processing sections matters since merging two
-// sections can make other sections, whose relocations now point to the same
-// section, mergeable. Graphs may contain cycles, which is common in COFF.
-// We need a sophisticated algorithm to do this properly and efficiently.
+// On Windows, ICF is enabled by default.
 //
-// What we do in this file is this. We split sections into groups. Sections
-// in the same group are considered identical.
-//
-// First, all sections are grouped by their "constant" values. Constant
-// values are values that are never changed by ICF, such as section contents,
-// section name, number of relocations, type and offset of each relocation,
-// etc. Because we do not care about some relocation targets in this step,
-// two sections in the same group may not be identical, but at least two
-// sections in different groups can never be identical.
-//
-// Then, we try to split each group by relocation targets. Relocations are
-// considered identical if and only if the relocation targets are in the
-// same group. Splitting a group may make more groups to be splittable,
-// because two relocations that were previously considered identical might
-// now point to different groups. We repeat this step until the convergence
-// is obtained.
-//
-// This algorithm is so-called "optimistic" algorithm described in
-// http://research.google.com/pubs/pub36912.html.
+// See ELF/ICF.cpp for the details about the algortihm.
 //
 //===----------------------------------------------------------------------===//
 
 #include "Chunks.h"
+#include "Error.h"
 #include "Symbols.h"
 #include "lld/Core/Parallel.h"
 #include "llvm/ADT/Hashing.h"
@@ -58,29 +34,34 @@ using namespace llvm;
 namespace lld {
 namespace coff {
 
-typedef std::vector<SectionChunk *>::iterator ChunkIterator;
-typedef bool (*Comparator)(const SectionChunk *, const SectionChunk *);
-
 class ICF {
 public:
   void run(const std::vector<Chunk *> &V);
 
 private:
-  static uint64_t getHash(SectionChunk *C);
-  static bool equalsConstant(const SectionChunk *A, const SectionChunk *B);
-  static bool equalsVariable(const SectionChunk *A, const SectionChunk *B);
-  bool forEachGroup(std::vector<SectionChunk *> &Chunks, Comparator Eq);
-  bool segregate(ChunkIterator Begin, ChunkIterator End, Comparator Eq);
+  void segregate(size_t Begin, size_t End, bool Constant);
 
-  std::atomic<uint64_t> NextID = { 1 };
-};
+  bool equalsConstant(const SectionChunk *A, const SectionChunk *B);
+  bool equalsVariable(const SectionChunk *A, const SectionChunk *B);
 
-// Entry point to ICF.
-void doICF(const std::vector<Chunk *> &Chunks) {
-  ICF().run(Chunks);
-}
+  uint32_t getHash(SectionChunk *C);
+  bool isEligible(SectionChunk *C);
+
+  size_t findBoundary(size_t Begin, size_t End);
+
+  void forEachColorRange(size_t Begin, size_t End,
+                         std::function<void(size_t, size_t)> Fn);
+
+  void forEachColor(std::function<void(size_t, size_t)> Fn);
+
+  std::vector<SectionChunk *> Chunks;
+  int Cnt = 0;
+  std::atomic<uint32_t> NextId = {1};
+  std::atomic<bool> Repeat = {false};
+};
 
-uint64_t ICF::getHash(SectionChunk *C) {
+// Returns a hash value for S.
+uint32_t ICF::getHash(SectionChunk *C) {
   return hash_combine(C->getPermissions(),
                       hash_value(C->SectionName),
                       C->NumRelocs,
@@ -89,16 +70,44 @@ uint64_t ICF::getHash(SectionChunk *C) {
                       C->Checksum);
 }
 
-bool ICF::equalsConstant(const SectionChunk *A, const SectionChunk *B) {
-  if (A->AssocChildren.size() != B->AssocChildren.size() ||
-      A->NumRelocs != B->NumRelocs) {
-    return false;
+// Returns true if section S is subject of ICF.
+bool ICF::isEligible(SectionChunk *C) {
+  bool Global = C->Sym && C->Sym->isExternal();
+  bool Writable = C->getPermissions() & llvm::COFF::IMAGE_SCN_MEM_WRITE;
+  return C->isCOMDAT() && C->isLive() && Global && !Writable;
+}
+
+// Split a range into smaller ranges by recoloring sections
+void ICF::segregate(size_t Begin, size_t End, bool Constant) {
+  while (Begin < End) {
+    // Divide [Begin, End) into two. Let Mid be the start index of the
+    // second group.
+    auto Bound = std::stable_partition(
+        Chunks.begin() + Begin + 1, Chunks.begin() + End, [&](SectionChunk *S) {
+          if (Constant)
+            return equalsConstant(Chunks[Begin], S);
+          return equalsVariable(Chunks[Begin], S);
+        });
+    size_t Mid = Bound - Chunks.begin();
+
+    // Split [Begin, End) into [Begin, Mid) and [Mid, End).
+    uint32_t Id = NextId++;
+    for (size_t I = Begin; I < Mid; ++I)
+      Chunks[I]->Color[(Cnt + 1) % 2] = Id;
+
+    // If we created a group, we need to iterate the main loop again.
+    if (Mid != End)
+      Repeat = true;
+
+    Begin = Mid;
   }
+}
 
-  // Compare associative sections.
-  for (size_t I = 0, E = A->AssocChildren.size(); I != E; ++I)
-    if (A->AssocChildren[I]->GroupID != B->AssocChildren[I]->GroupID)
-      return false;
+// Compare "non-moving" part of two sections, namely everything
+// except relocation targets.
+bool ICF::equalsConstant(const SectionChunk *A, const SectionChunk *B) {
+  if (A->NumRelocs != B->NumRelocs)
+    return false;
 
   // Compare relocations.
   auto Eq = [&](const coff_relocation &R1, const coff_relocation &R2) {
@@ -106,14 +115,14 @@ bool ICF::equalsConstant(const SectionChunk *A, const SectionChunk *B) {
         R1.VirtualAddress != R2.VirtualAddress) {
       return false;
     }
-    SymbolBody *B1 = A->File->getSymbolBody(R1.SymbolTableIndex)->repl();
-    SymbolBody *B2 = B->File->getSymbolBody(R2.SymbolTableIndex)->repl();
+    SymbolBody *B1 = A->File->getSymbolBody(R1.SymbolTableIndex);
+    SymbolBody *B2 = B->File->getSymbolBody(R2.SymbolTableIndex);
     if (B1 == B2)
       return true;
     if (auto *D1 = dyn_cast<DefinedRegular>(B1))
       if (auto *D2 = dyn_cast<DefinedRegular>(B2))
         return D1->getValue() == D2->getValue() &&
-               D1->getChunk()->GroupID == D2->getChunk()->GroupID;
+               D1->getChunk()->Color[Cnt % 2] == D2->getChunk()->Color[Cnt % 2];
     return false;
   };
   if (!std::equal(A->Relocs.begin(), A->Relocs.end(), B->Relocs.begin(), Eq))
@@ -128,54 +137,57 @@ bool ICF::equalsConstant(const SectionChunk *A, const SectionChunk *B) {
          A->getContents() == B->getContents();
 }
 
+// Compare "moving" part of two sections, namely relocation targets.
 bool ICF::equalsVariable(const SectionChunk *A, const SectionChunk *B) {
-  // Compare associative sections.
-  for (size_t I = 0, E = A->AssocChildren.size(); I != E; ++I)
-    if (A->AssocChildren[I]->GroupID != B->AssocChildren[I]->GroupID)
-      return false;
-
   // Compare relocations.
   auto Eq = [&](const coff_relocation &R1, const coff_relocation &R2) {
-    SymbolBody *B1 = A->File->getSymbolBody(R1.SymbolTableIndex)->repl();
-    SymbolBody *B2 = B->File->getSymbolBody(R2.SymbolTableIndex)->repl();
+    SymbolBody *B1 = A->File->getSymbolBody(R1.SymbolTableIndex);
+    SymbolBody *B2 = B->File->getSymbolBody(R2.SymbolTableIndex);
     if (B1 == B2)
       return true;
     if (auto *D1 = dyn_cast<DefinedRegular>(B1))
       if (auto *D2 = dyn_cast<DefinedRegular>(B2))
-        return D1->getChunk()->GroupID == D2->getChunk()->GroupID;
+        return D1->getChunk()->Color[Cnt % 2] == D2->getChunk()->Color[Cnt % 2];
     return false;
   };
   return std::equal(A->Relocs.begin(), A->Relocs.end(), B->Relocs.begin(), Eq);
 }
 
-bool ICF::segregate(ChunkIterator Begin, ChunkIterator End, Comparator Eq) {
-  bool R = false;
-  for (auto It = Begin;;) {
-    SectionChunk *Head = *It;
-    auto Bound = std::partition(It + 1, End, [&](SectionChunk *SC) {
-      return Eq(Head, SC);
-    });
-    if (Bound == End)
-      return R;
-    uint64_t ID = NextID++;
-    std::for_each(It, Bound, [&](SectionChunk *SC) { SC->GroupID = ID; });
-    It = Bound;
-    R = true;
+size_t ICF::findBoundary(size_t Begin, size_t End) {
+  for (size_t I = Begin + 1; I < End; ++I)
+    if (Chunks[Begin]->Color[Cnt % 2] != Chunks[I]->Color[Cnt % 2])
+      return I;
+  return End;
+}
+
+void ICF::forEachColorRange(size_t Begin, size_t End,
+                            std::function<void(size_t, size_t)> Fn) {
+  if (Begin > 0)
+    Begin = findBoundary(Begin - 1, End);
+
+  while (Begin < End) {
+    size_t Mid = findBoundary(Begin, Chunks.size());
+    Fn(Begin, Mid);
+    Begin = Mid;
   }
 }
 
-bool ICF::forEachGroup(std::vector<SectionChunk *> &Chunks, Comparator Eq) {
-  bool R = false;
-  for (auto It = Chunks.begin(), End = Chunks.end(); It != End;) {
-    SectionChunk *Head = *It;
-    auto Bound = std::find_if(It + 1, End, [&](SectionChunk *SC) {
-      return SC->GroupID != Head->GroupID;
-    });
-    if (segregate(It, Bound, Eq))
-      R = true;
-    It = Bound;
+// Call Fn on each color group.
+void ICF::forEachColor(std::function<void(size_t, size_t)> Fn) {
+  // If the number of sections are too small to use threading,
+  // call Fn sequentially.
+  if (Chunks.size() < 1024) {
+    forEachColorRange(0, Chunks.size(), Fn);
+    return;
   }
-  return R;
+
+  // Split sections into 256 shards and call Fn in parallel.
+  size_t NumShards = 256;
+  size_t Step = Chunks.size() / NumShards;
+  parallel_for(size_t(0), NumShards, [&](size_t I) {
+    forEachColorRange(I * Step, (I + 1) * Step, Fn);
+  });
+  forEachColorRange(Step * NumShards, Chunks.size(), Fn);
 }
 
 // Merge identical COMDAT sections.
@@ -183,62 +195,62 @@ bool ICF::forEachGroup(std::vector<SectionChunk *> &Chunks, Comparator Eq) {
 // contents and relocations are all the same.
 void ICF::run(const std::vector<Chunk *> &Vec) {
   // Collect only mergeable sections and group by hash value.
-  parallel_for_each(Vec.begin(), Vec.end(), [&](Chunk *C) {
-    if (auto *SC = dyn_cast<SectionChunk>(C)) {
-      bool Global = SC->Sym && SC->Sym->isExternal();
-      bool Writable = SC->getPermissions() & llvm::COFF::IMAGE_SCN_MEM_WRITE;
-      if (SC->isCOMDAT() && SC->isLive() && Global && !Writable)
-        SC->GroupID = getHash(SC) | (uint64_t(1) << 63);
-    }
-  });
-  std::vector<SectionChunk *> Chunks;
   for (Chunk *C : Vec) {
-    if (auto *SC = dyn_cast<SectionChunk>(C)) {
-      if (SC->GroupID) {
-        Chunks.push_back(SC);
-      } else {
-        SC->GroupID = NextID++;
-      }
+    auto *SC = dyn_cast<SectionChunk>(C);
+    if (!SC)
+      continue;
+
+    if (isEligible(SC)) {
+      // Set MSB to 1 to avoid collisions with non-hash colors.
+      SC->Color[0] = getHash(SC) | (1 << 31);
+      Chunks.push_back(SC);
+    } else {
+      SC->Color[0] = NextId++;
     }
   }
 
+  if (Chunks.empty())
+    return;
+
   // From now on, sections in Chunks are ordered so that sections in
   // the same group are consecutive in the vector.
-  std::sort(Chunks.begin(), Chunks.end(),
-            [](SectionChunk *A, SectionChunk *B) {
-              return A->GroupID < B->GroupID;
-            });
-
-  // Split groups until we get a convergence.
-  int Cnt = 1;
-  forEachGroup(Chunks, equalsConstant);
-
-  for (;;) {
-    if (!forEachGroup(Chunks, equalsVariable))
-      break;
+  std::stable_sort(Chunks.begin(), Chunks.end(),
+                   [](SectionChunk *A, SectionChunk *B) {
+                     return A->Color[0] < B->Color[0];
+                   });
+
+  // Compare static contents and assign unique IDs for each static content.
+  forEachColor([&](size_t Begin, size_t End) { segregate(Begin, End, true); });
+  ++Cnt;
+
+  // Split groups by comparing relocations until convergence is obtained.
+  do {
+    Repeat = false;
+    forEachColor(
+        [&](size_t Begin, size_t End) { segregate(Begin, End, false); });
     ++Cnt;
-  }
+  } while (Repeat);
+
   if (Config->Verbose)
-    llvm::outs() << "\nICF needed " << Cnt << " iterations.\n";
-
-  // Merge sections in the same group.
-  for (auto It = Chunks.begin(), End = Chunks.end(); It != End;) {
-    SectionChunk *Head = *It++;
-    auto Bound = std::find_if(It, End, [&](SectionChunk *SC) {
-      return Head->GroupID != SC->GroupID;
-    });
-    if (It == Bound)
-      continue;
+    outs() << "\nICF needed " << Cnt << " iterations\n";
+
+  // Merge sections in the same colors.
+  forEachColor([&](size_t Begin, size_t End) {
+    if (End - Begin == 1)
+      return;
+
     if (Config->Verbose)
-      llvm::outs() << "Selected " << Head->getDebugName() << "\n";
-    while (It != Bound) {
-      SectionChunk *SC = *It++;
+      outs() << "Selected " << Chunks[Begin]->getDebugName() << "\n";
+    for (size_t I = Begin + 1; I < End; ++I) {
       if (Config->Verbose)
-        llvm::outs() << "  Removed " << SC->getDebugName() << "\n";
-      Head->replace(SC);
+        outs() << "  Removed " << Chunks[I]->getDebugName() << "\n";
+      Chunks[Begin]->replace(Chunks[I]);
     }
-  }
+  });
 }
 
+// Entry point to ICF.
+void doICF(const std::vector<Chunk *> &Chunks) { ICF().run(Chunks); }
+
 } // namespace coff
 } // namespace lld
diff --git a/COFF/InputFiles.cpp b/COFF/InputFiles.cpp
index ff26826371fa..0a97c2185f89 100644
--- a/COFF/InputFiles.cpp
+++ b/COFF/InputFiles.cpp
@@ -7,11 +7,15 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "InputFiles.h"
 #include "Chunks.h"
 #include "Config.h"
+#include "Driver.h"
 #include "Error.h"
-#include "InputFiles.h"
+#include "Memory.h"
+#include "SymbolTable.h"
 #include "Symbols.h"
+#include "llvm-c/lto.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/Triple.h"
 #include "llvm/ADT/Twine.h"
@@ -26,88 +30,58 @@
 #include "llvm/Support/ErrorOr.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Target/TargetOptions.h"
-#include "llvm-c/lto.h"
 #include <cstring>
 #include <system_error>
 #include <utility>
 
+using namespace llvm;
 using namespace llvm::COFF;
 using namespace llvm::object;
 using namespace llvm::support::endian;
 
 using llvm::Triple;
 using llvm::support::ulittle32_t;
+using llvm::sys::fs::file_magic;
+using llvm::sys::fs::identify_magic;
 
 namespace lld {
 namespace coff {
 
-int InputFile::NextIndex = 0;
-llvm::LLVMContext BitcodeFile::Context;
-
-// Returns the last element of a path, which is supposed to be a filename.
-static StringRef getBasename(StringRef Path) {
-  size_t Pos = Path.find_last_of("\\/");
-  if (Pos == StringRef::npos)
-    return Path;
-  return Path.substr(Pos + 1);
-}
+LLVMContext BitcodeFile::Context;
 
-// Returns a string in the format of "foo.obj" or "foo.obj(bar.lib)".
-std::string InputFile::getShortName() {
-  if (ParentName == "")
-    return getName().lower();
-  std::string Res = (getBasename(ParentName) + "(" +
-                     getBasename(getName()) + ")").str();
-  return StringRef(Res).lower();
-}
+ArchiveFile::ArchiveFile(MemoryBufferRef M) : InputFile(ArchiveKind, M) {}
 
 void ArchiveFile::parse() {
   // Parse a MemoryBufferRef as an archive file.
-  File = check(Archive::create(MB), "failed to parse static library");
-
-  // Allocate a buffer for Lazy objects.
-  size_t NumSyms = File->getNumberOfSymbols();
-  LazySymbols.reserve(NumSyms);
+  File = check(Archive::create(MB), toString(this));
 
   // Read the symbol table to construct Lazy objects.
   for (const Archive::Symbol &Sym : File->symbols())
-    LazySymbols.emplace_back(this, Sym);
-
-  // Seen is a map from member files to boolean values. Initially
-  // all members are mapped to false, which indicates all these files
-  // are not read yet.
-  Error Err;
-  for (auto &Child : File->children(Err))
-    Seen[Child.getChildOffset()].clear();
-  if (Err)
-    fatal(Err, "failed to parse static library");
+    Symtab->addLazy(this, Sym);
 }
 
 // Returns a buffer pointing to a member file containing a given symbol.
-// This function is thread-safe.
-MemoryBufferRef ArchiveFile::getMember(const Archive::Symbol *Sym) {
+void ArchiveFile::addMember(const Archive::Symbol *Sym) {
   const Archive::Child &C =
       check(Sym->getMember(),
             "could not get the member for symbol " + Sym->getName());
 
   // Return an empty buffer if we have already returned the same buffer.
-  if (Seen[C.getChildOffset()].test_and_set())
-    return MemoryBufferRef();
-  return check(C.getMemoryBufferRef(),
-               "could not get the buffer for the member defining symbol " +
-                   Sym->getName());
+  if (!Seen.insert(C.getChildOffset()).second)
+    return;
+
+  Driver->enqueueArchiveMember(C, Sym->getName(), getName());
 }
 
 void ObjectFile::parse() {
   // Parse a memory buffer as a COFF file.
-  std::unique_ptr<Binary> Bin =
-      check(createBinary(MB), "failed to parse object file");
+  std::unique_ptr<Binary> Bin = check(createBinary(MB), toString(this));
 
   if (auto *Obj = dyn_cast<COFFObjectFile>(Bin.get())) {
     Bin.release();
     COFFObj.reset(Obj);
   } else {
-    fatal(getName() + " is not a COFF file");
+    fatal(toString(this) + " is not a COFF file");
   }
 
   // Read section and symbol tables.
@@ -137,13 +111,28 @@ void ObjectFile::initializeChunks() {
       Directives = std::string((const char *)Data.data(), Data.size());
       continue;
     }
-    // Skip non-DWARF debug info. MSVC linker converts the sections into
-    // a PDB file, but we don't support that.
-    if (Name == ".debug" || Name.startswith(".debug$"))
-      continue;
-    // We want to preserve DWARF debug sections only when /debug is on.
+
+    // Object files may have DWARF debug info or MS CodeView debug info
+    // (or both).
+    //
+    // DWARF sections don't need any special handling from the perspective
+    // of the linker; they are just a data section containing relocations.
+    // We can just link them to complete debug info.
+    //
+    // CodeView needs a linker support. We need to interpret and debug
+    // info, and then write it to a separate .pdb file.
+
+    // Ignore debug info unless /debug is given.
     if (!Config->Debug && Name.startswith(".debug"))
       continue;
+
+    // CodeView sections are stored to a different vector because they are
+    // not linked in the regular manner.
+    if (Name == ".debug" || Name.startswith(".debug$")) {
+      DebugChunks.push_back(new (Alloc) SectionChunk(this, Sec));
+      continue;
+    }
+
     if (Sec->Characteristics & llvm::COFF::IMAGE_SCN_LNK_REMOVE)
       continue;
     auto *C = new (Alloc) SectionChunk(this, Sec);
@@ -156,12 +145,14 @@ void ObjectFile::initializeSymbols() {
   uint32_t NumSymbols = COFFObj->getNumberOfSymbols();
   SymbolBodies.reserve(NumSymbols);
   SparseSymbolBodies.resize(NumSymbols);
-  llvm::SmallVector<std::pair<Undefined *, uint32_t>, 8> WeakAliases;
+  SmallVector<std::pair<SymbolBody *, uint32_t>, 8> WeakAliases;
   int32_t LastSectionNumber = 0;
   for (uint32_t I = 0; I < NumSymbols; ++I) {
     // Get a COFFSymbolRef object.
-    COFFSymbolRef Sym =
-        check(COFFObj->getSymbol(I), "broken object file: " + getName());
+    ErrorOr<COFFSymbolRef> SymOrErr = COFFObj->getSymbol(I);
+    if (!SymOrErr)
+      fatal(SymOrErr.getError(), "broken object file: " + toString(this));
+    COFFSymbolRef Sym = *SymOrErr;
 
     const void *AuxP = nullptr;
     if (Sym.getNumberOfAuxSymbols())
@@ -175,7 +166,7 @@ void ObjectFile::initializeSymbols() {
       Body = createUndefined(Sym);
       uint32_t TagIndex =
           static_cast<const coff_aux_weak_external *>(AuxP)->TagIndex;
-      WeakAliases.emplace_back((Undefined *)Body, TagIndex);
+      WeakAliases.emplace_back(Body, TagIndex);
     } else {
       Body = createDefined(Sym, AuxP, IsFirst);
     }
@@ -186,23 +177,30 @@ void ObjectFile::initializeSymbols() {
     I += Sym.getNumberOfAuxSymbols();
     LastSectionNumber = Sym.getSectionNumber();
   }
-  for (auto WeakAlias : WeakAliases)
-    WeakAlias.first->WeakAlias = SparseSymbolBodies[WeakAlias.second];
+  for (auto WeakAlias : WeakAliases) {
+    auto *U = dyn_cast<Undefined>(WeakAlias.first);
+    if (!U)
+      continue;
+    // Report an error if two undefined symbols have different weak aliases.
+    if (U->WeakAlias && U->WeakAlias != SparseSymbolBodies[WeakAlias.second])
+      Symtab->reportDuplicate(U->symbol(), this);
+    U->WeakAlias = SparseSymbolBodies[WeakAlias.second];
+  }
 }
 
-Undefined *ObjectFile::createUndefined(COFFSymbolRef Sym) {
+SymbolBody *ObjectFile::createUndefined(COFFSymbolRef Sym) {
   StringRef Name;
   COFFObj->getSymbolName(Sym, Name);
-  return new (Alloc) Undefined(Name);
+  return Symtab->addUndefined(Name, this, Sym.isWeakExternal())->body();
 }
 
-Defined *ObjectFile::createDefined(COFFSymbolRef Sym, const void *AuxP,
-                                   bool IsFirst) {
+SymbolBody *ObjectFile::createDefined(COFFSymbolRef Sym, const void *AuxP,
+                                      bool IsFirst) {
   StringRef Name;
   if (Sym.isCommon()) {
     auto *C = new (Alloc) CommonChunk(Sym);
     Chunks.push_back(C);
-    return new (Alloc) DefinedCommon(this, Sym, C);
+    return Symtab->addCommon(this, Sym, C)->body();
   }
   if (Sym.isAbsolute()) {
     COFFObj->getSymbolName(Sym, Name);
@@ -215,7 +213,10 @@ Defined *ObjectFile::createDefined(COFFSymbolRef Sym, const void *AuxP,
         SEHCompat = true;
       return nullptr;
     }
-    return new (Alloc) DefinedAbsolute(Name, Sym);
+    if (Sym.isExternal())
+      return Symtab->addAbsolute(Name, Sym)->body();
+    else
+      return new (Alloc) DefinedAbsolute(Name, Sym);
   }
   int32_t SectionNumber = Sym.getSectionNumber();
   if (SectionNumber == llvm::COFF::IMAGE_SYM_DEBUG)
@@ -223,12 +224,12 @@ Defined *ObjectFile::createDefined(COFFSymbolRef Sym, const void *AuxP,
 
   // Reserved sections numbers don't have contents.
   if (llvm::COFF::isReservedSectionNumber(SectionNumber))
-    fatal("broken object file: " + getName());
+    fatal("broken object file: " + toString(this));
 
   // This symbol references a section which is not present in the section
   // header.
   if ((uint32_t)SectionNumber >= SparseChunks.size())
-    fatal("broken object file: " + getName());
+    fatal("broken object file: " + toString(this));
 
   // Nothing else to do without a section chunk.
   auto *SC = cast_or_null<SectionChunk>(SparseChunks[SectionNumber]);
@@ -245,7 +246,11 @@ Defined *ObjectFile::createDefined(COFFSymbolRef Sym, const void *AuxP,
     SC->Checksum = Aux->CheckSum;
   }
 
-  auto *B = new (Alloc) DefinedRegular(this, Sym, SC);
+  DefinedRegular *B;
+  if (Sym.isExternal())
+    B = cast<DefinedRegular>(Symtab->addRegular(this, Sym, SC)->body());
+  else
+    B = new (Alloc) DefinedRegular(this, Sym, SC);
   if (SC->isCOMDAT() && Sym.getValue() == 0 && !AuxP)
     SC->setSymbol(B);
 
@@ -307,28 +312,29 @@ void ImportFile::parse() {
     ExtName = ExtName.substr(0, ExtName.find('@'));
     break;
   }
-  ImpSym = new (Alloc) DefinedImportData(DLLName, ImpName, ExtName, Hdr);
-  SymbolBodies.push_back(ImpSym);
+
+  this->Hdr = Hdr;
+  ExternalName = ExtName;
+
+  ImpSym = cast<DefinedImportData>(
+      Symtab->addImportData(ImpName, this)->body());
 
   // If type is function, we need to create a thunk which jump to an
   // address pointed by the __imp_ symbol. (This allows you to call
   // DLL functions just like regular non-DLL functions.)
   if (Hdr->getType() != llvm::COFF::IMPORT_CODE)
     return;
-  ThunkSym = new (Alloc) DefinedImportThunk(Name, ImpSym, Hdr->Machine);
-  SymbolBodies.push_back(ThunkSym);
+  ThunkSym = cast<DefinedImportThunk>(
+      Symtab->addImportThunk(Name, ImpSym, Hdr->Machine)->body());
 }
 
 void BitcodeFile::parse() {
-  // Usually parse() is thread-safe, but bitcode file is an exception.
-  std::lock_guard<std::mutex> Lock(Mu);
-
   Context.enableDebugTypeODRUniquing();
   ErrorOr<std::unique_ptr<LTOModule>> ModOrErr = LTOModule::createFromBuffer(
       Context, MB.getBufferStart(), MB.getBufferSize(), llvm::TargetOptions());
   M = check(std::move(ModOrErr), "could not create LTO module");
 
-  llvm::StringSaver Saver(Alloc);
+  StringSaver Saver(Alloc);
   for (unsigned I = 0, E = M->getSymbolCount(); I != E; ++I) {
     lto_symbol_attributes Attrs = M->getSymbolAttributes(I);
     if ((Attrs & LTO_SYMBOL_SCOPE_MASK) == LTO_SYMBOL_SCOPE_INTERNAL)
@@ -337,15 +343,15 @@ void BitcodeFile::parse() {
     StringRef SymName = Saver.save(M->getSymbolName(I));
     int SymbolDef = Attrs & LTO_SYMBOL_DEFINITION_MASK;
     if (SymbolDef == LTO_SYMBOL_DEFINITION_UNDEFINED) {
-      SymbolBodies.push_back(new (Alloc) Undefined(SymName));
+      SymbolBodies.push_back(Symtab->addUndefined(SymName, this, false)->body());
     } else {
       bool Replaceable =
           (SymbolDef == LTO_SYMBOL_DEFINITION_TENTATIVE || // common
            (Attrs & LTO_SYMBOL_COMDAT) ||                  // comdat
            (SymbolDef == LTO_SYMBOL_DEFINITION_WEAK &&     // weak external
             (Attrs & LTO_SYMBOL_ALIAS)));
-      SymbolBodies.push_back(new (Alloc) DefinedBitcode(this, SymName,
-                                                        Replaceable));
+      SymbolBodies.push_back(
+          Symtab->addBitcode(this, SymName, Replaceable)->body());
     }
   }
 
@@ -367,7 +373,26 @@ MachineTypes BitcodeFile::getMachineType() {
   }
 }
 
-std::mutex BitcodeFile::Mu;
+// Returns the last element of a path, which is supposed to be a filename.
+static StringRef getBasename(StringRef Path) {
+  size_t Pos = Path.find_last_of("\\/");
+  if (Pos == StringRef::npos)
+    return Path;
+  return Path.substr(Pos + 1);
+}
+
+// Returns a string in the format of "foo.obj" or "foo.obj(bar.lib)".
+std::string toString(InputFile *File) {
+  if (!File)
+    return "(internal)";
+  if (File->ParentName.empty())
+    return File->getName().lower();
+
+  std::string Res =
+      (getBasename(File->ParentName) + "(" + getBasename(File->getName()) + ")")
+          .str();
+  return StringRef(Res).lower();
+}
 
 } // namespace coff
 } // namespace lld
diff --git a/COFF/InputFiles.h b/COFF/InputFiles.h
index 0ec01b5075f9..498a1743e985 100644
--- a/COFF/InputFiles.h
+++ b/COFF/InputFiles.h
@@ -12,13 +12,13 @@
 
 #include "lld/Core/LLVM.h"
 #include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/DenseSet.h"
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/LTO/legacy/LTOModule.h"
 #include "llvm/Object/Archive.h"
 #include "llvm/Object/COFF.h"
 #include "llvm/Support/StringSaver.h"
 #include <memory>
-#include <mutex>
 #include <set>
 #include <vector>
 
@@ -31,6 +31,7 @@ using llvm::COFF::MachineTypes;
 using llvm::object::Archive;
 using llvm::object::COFFObjectFile;
 using llvm::object::COFFSymbolRef;
+using llvm::object::coff_import_header;
 using llvm::object::coff_section;
 
 class Chunk;
@@ -38,6 +39,8 @@ class Defined;
 class DefinedImportData;
 class DefinedImportThunk;
 class Lazy;
+class SectionChunk;
+struct Symbol;
 class SymbolBody;
 class Undefined;
 
@@ -51,67 +54,44 @@ public:
   // Returns the filename.
   StringRef getName() { return MB.getBufferIdentifier(); }
 
-  // Returns symbols defined by this file.
-  virtual std::vector<SymbolBody *> &getSymbols() = 0;
-
   // Reads a file (the constructor doesn't do that).
   virtual void parse() = 0;
 
   // Returns the CPU type this file was compiled to.
   virtual MachineTypes getMachineType() { return IMAGE_FILE_MACHINE_UNKNOWN; }
 
-  // Returns a short, human-friendly filename. If this is a member of
-  // an archive file, a returned value includes parent's filename.
-  // Used for logging or debugging.
-  std::string getShortName();
-
-  // Sets a parent filename if this file is created from an archive.
-  void setParentName(StringRef N) { ParentName = N; }
+  // An archive file name if this file is created from an archive.
+  StringRef ParentName;
 
   // Returns .drectve section contents if exist.
   StringRef getDirectives() { return StringRef(Directives).trim(); }
 
-  // Each file has a unique index. The index number is used to
-  // resolve ties in symbol resolution.
-  int Index;
-  static int NextIndex;
-
 protected:
-  InputFile(Kind K, MemoryBufferRef M)
-      : Index(NextIndex++), MB(M), FileKind(K) {}
+  InputFile(Kind K, MemoryBufferRef M) : MB(M), FileKind(K) {}
 
   MemoryBufferRef MB;
   std::string Directives;
 
 private:
   const Kind FileKind;
-  StringRef ParentName;
 };
 
 // .lib or .a file.
 class ArchiveFile : public InputFile {
 public:
-  explicit ArchiveFile(MemoryBufferRef M) : InputFile(ArchiveKind, M) {}
+  explicit ArchiveFile(MemoryBufferRef M);
   static bool classof(const InputFile *F) { return F->kind() == ArchiveKind; }
   void parse() override;
 
-  // Returns a memory buffer for a given symbol. An empty memory buffer
-  // is returned if we have already returned the same memory buffer.
-  // (So that we don't instantiate same members more than once.)
-  MemoryBufferRef getMember(const Archive::Symbol *Sym);
-
-  llvm::MutableArrayRef<Lazy> getLazySymbols() { return LazySymbols; }
-
-  // All symbols returned by ArchiveFiles are of Lazy type.
-  std::vector<SymbolBody *> &getSymbols() override {
-    llvm_unreachable("internal fatal");
-  }
+  // Enqueues an archive member load for the given symbol. If we've already
+  // enqueued a load for the same archive member, this function does nothing,
+  // which ensures that we don't load the same member more than once.
+  void addMember(const Archive::Symbol *Sym);
 
 private:
   std::unique_ptr<Archive> File;
   std::string Filename;
-  std::vector<Lazy> LazySymbols;
-  std::map<uint64_t, std::atomic_flag> Seen;
+  llvm::DenseSet<uint64_t> Seen;
 };
 
 // .obj or .o file. This may be a member of an archive file.
@@ -122,7 +102,8 @@ public:
   void parse() override;
   MachineTypes getMachineType() override;
   std::vector<Chunk *> &getChunks() { return Chunks; }
-  std::vector<SymbolBody *> &getSymbols() override { return SymbolBodies; }
+  std::vector<SectionChunk *> &getDebugChunks() { return DebugChunks; }
+  std::vector<SymbolBody *> &getSymbols() { return SymbolBodies; }
 
   // Returns a SymbolBody object for the SymbolIndex'th symbol in the
   // underlying object file.
@@ -146,8 +127,8 @@ private:
   void initializeSymbols();
   void initializeSEH();
 
-  Defined *createDefined(COFFSymbolRef Sym, const void *Aux, bool IsFirst);
-  Undefined *createUndefined(COFFSymbolRef Sym);
+  SymbolBody *createDefined(COFFSymbolRef Sym, const void *Aux, bool IsFirst);
+  SymbolBody *createUndefined(COFFSymbolRef Sym);
 
   std::unique_ptr<COFFObjectFile> COFFObj;
   llvm::BumpPtrAllocator Alloc;
@@ -157,6 +138,9 @@ private:
   // chunks and non-section chunks for common symbols.
   std::vector<Chunk *> Chunks;
 
+  // CodeView debug info sections.
+  std::vector<SectionChunk *> DebugChunks;
+
   // This vector contains the same chunks as Chunks, but they are
   // indexed such that you can get a SectionChunk by section index.
   // Nonexistent section indices are filled with null pointers.
@@ -182,7 +166,6 @@ public:
   explicit ImportFile(MemoryBufferRef M)
       : InputFile(ImportKind, M), StringAlloc(StringAllocAux) {}
   static bool classof(const InputFile *F) { return F->kind() == ImportKind; }
-  std::vector<SymbolBody *> &getSymbols() override { return SymbolBodies; }
 
   DefinedImportData *ImpSym = nullptr;
   DefinedImportThunk *ThunkSym = nullptr;
@@ -191,10 +174,14 @@ public:
 private:
   void parse() override;
 
-  std::vector<SymbolBody *> SymbolBodies;
   llvm::BumpPtrAllocator Alloc;
   llvm::BumpPtrAllocator StringAllocAux;
   llvm::StringSaver StringAlloc;
+
+public:
+  StringRef ExternalName;
+  const coff_import_header *Hdr;
+  Chunk *Location = nullptr;
 };
 
 // Used for LTO.
@@ -202,7 +189,7 @@ class BitcodeFile : public InputFile {
 public:
   explicit BitcodeFile(MemoryBufferRef M) : InputFile(BitcodeKind, M) {}
   static bool classof(const InputFile *F) { return F->kind() == BitcodeKind; }
-  std::vector<SymbolBody *> &getSymbols() override { return SymbolBodies; }
+  std::vector<SymbolBody *> &getSymbols() { return SymbolBodies; }
   MachineTypes getMachineType() override;
   std::unique_ptr<LTOModule> takeModule() { return std::move(M); }
 
@@ -214,9 +201,10 @@ private:
   std::vector<SymbolBody *> SymbolBodies;
   llvm::BumpPtrAllocator Alloc;
   std::unique_ptr<LTOModule> M;
-  static std::mutex Mu;
 };
 
+std::string toString(InputFile *File);
+
 } // namespace coff
 } // namespace lld
 
diff --git a/COFF/Librarian.cpp b/COFF/Librarian.cpp
index 25fb4a87b3eb..4c597fad7345 100644
--- a/COFF/Librarian.cpp
+++ b/COFF/Librarian.cpp
@@ -54,7 +54,7 @@ static uint16_t getImgRelRelocation() {
   }
 }
 
-template <class T> void append(std::vector<uint8_t> &B, const T &Data) {
+template <class T> static void append(std::vector<uint8_t> &B, const T &Data) {
   size_t S = B.size();
   B.resize(S + sizeof(T));
   memcpy(&B[S], &Data, sizeof(T));
@@ -352,15 +352,16 @@ ObjectFactory::createNullImportDescriptor(std::vector<uint8_t> &Buffer) {
 NewArchiveMember ObjectFactory::createNullThunk(std::vector<uint8_t> &Buffer) {
   static const uint32_t NumberOfSections = 2;
   static const uint32_t NumberOfSymbols = 1;
+  uint32_t VASize = is32bit() ? 4 : 8;
 
   // COFF Header
   coff_file_header Header{
       u16(Config->Machine), u16(NumberOfSections), u32(0),
       u32(sizeof(Header) + (NumberOfSections * sizeof(coff_section)) +
           // .idata$5
-          sizeof(export_address_table_entry) +
+          VASize +
           // .idata$4
-          sizeof(export_address_table_entry)),
+          VASize),
       u32(NumberOfSymbols), u16(0),
       u16(is32bit() ? IMAGE_FILE_32BIT_MACHINE : 0),
   };
@@ -371,36 +372,40 @@ NewArchiveMember ObjectFactory::createNullThunk(std::vector<uint8_t> &Buffer) {
       {{'.', 'i', 'd', 'a', 't', 'a', '$', '5'},
        u32(0),
        u32(0),
-       u32(sizeof(export_address_table_entry)),
+       u32(VASize),
        u32(sizeof(coff_file_header) + NumberOfSections * sizeof(coff_section)),
        u32(0),
        u32(0),
        u16(0),
        u16(0),
-       u32(IMAGE_SCN_ALIGN_4BYTES | IMAGE_SCN_CNT_INITIALIZED_DATA |
-           IMAGE_SCN_MEM_READ | IMAGE_SCN_MEM_WRITE)},
+       u32((is32bit() ? IMAGE_SCN_ALIGN_4BYTES : IMAGE_SCN_ALIGN_8BYTES) |
+           IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ |
+           IMAGE_SCN_MEM_WRITE)},
       {{'.', 'i', 'd', 'a', 't', 'a', '$', '4'},
        u32(0),
        u32(0),
-       u32(sizeof(export_address_table_entry)),
+       u32(VASize),
        u32(sizeof(coff_file_header) + NumberOfSections * sizeof(coff_section) +
-           sizeof(export_address_table_entry)),
+           VASize),
        u32(0),
        u32(0),
        u16(0),
        u16(0),
-       u32(IMAGE_SCN_ALIGN_4BYTES | IMAGE_SCN_CNT_INITIALIZED_DATA |
-           IMAGE_SCN_MEM_READ | IMAGE_SCN_MEM_WRITE)},
+       u32((is32bit() ? IMAGE_SCN_ALIGN_4BYTES : IMAGE_SCN_ALIGN_8BYTES) |
+           IMAGE_SCN_CNT_INITIALIZED_DATA | IMAGE_SCN_MEM_READ |
+           IMAGE_SCN_MEM_WRITE)},
   };
   append(Buffer, SectionTable);
 
-  // .idata$5
-  static const export_address_table_entry ILT{u32(0)};
-  append(Buffer, ILT);
+  // .idata$5, ILT
+  append(Buffer, u32(0));
+  if (!is32bit())
+    append(Buffer, u32(0));
 
-  // .idata$4
-  static const export_address_table_entry IAT{u32(0)};
-  append(Buffer, IAT);
+  // .idata$4, IAT
+  append(Buffer, u32(0));
+  if (!is32bit())
+    append(Buffer, u32(0));
 
   // Symbol Table
   coff_symbol16 SymbolTable[NumberOfSymbols] = {
@@ -458,7 +463,7 @@ void lld::coff::writeImportLibrary() {
   std::vector<NewArchiveMember> Members;
 
   std::string Path = getImplibPath();
-  std::string DLLName = llvm::sys::path::filename(Config->OutputFile);
+  std::string DLLName = sys::path::filename(Config->OutputFile);
   ObjectFactory OF(DLLName);
 
   std::vector<uint8_t> ImportDescriptor;
diff --git a/COFF/MarkLive.cpp b/COFF/MarkLive.cpp
index 0870986ad81a..0156d238b672 100644
--- a/COFF/MarkLive.cpp
+++ b/COFF/MarkLive.cpp
@@ -38,8 +38,8 @@ void markLive(const std::vector<Chunk *> &Chunks) {
   };
 
   // Add GC root chunks.
-  for (Undefined *U : Config->GCRoot)
-    if (auto *D = dyn_cast<DefinedRegular>(U->repl()))
+  for (SymbolBody *B : Config->GCRoot)
+    if (auto *D = dyn_cast<DefinedRegular>(B))
       Enqueue(D->getChunk());
 
   while (!Worklist.empty()) {
@@ -48,7 +48,7 @@ void markLive(const std::vector<Chunk *> &Chunks) {
 
     // Mark all symbols listed in the relocation table for this section.
     for (SymbolBody *S : SC->symbols())
-      if (auto *D = dyn_cast<DefinedRegular>(S->repl()))
+      if (auto *D = dyn_cast<DefinedRegular>(S))
         Enqueue(D->getChunk());
 
     // Mark associative sections if any.
diff --git a/COFF/Memory.h b/COFF/Memory.h
new file mode 100644
index 000000000000..526f11344a09
--- /dev/null
+++ b/COFF/Memory.h
@@ -0,0 +1,52 @@
+//===- Memory.h -------------------------------------------------*- C++ -*-===//
+//
+//                             The LLVM Linker
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// See ELF/Memory.h
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLD_COFF_MEMORY_H
+#define LLD_COFF_MEMORY_H
+
+#include "llvm/Support/Allocator.h"
+#include "llvm/Support/StringSaver.h"
+#include <vector>
+
+namespace lld {
+namespace coff {
+
+extern llvm::BumpPtrAllocator BAlloc;
+extern llvm::StringSaver Saver;
+
+struct SpecificAllocBase {
+  SpecificAllocBase() { Instances.push_back(this); }
+  virtual ~SpecificAllocBase() = default;
+  virtual void reset() = 0;
+  static std::vector<SpecificAllocBase *> Instances;
+};
+
+template <class T> struct SpecificAlloc : public SpecificAllocBase {
+  void reset() override { Alloc.DestroyAll(); }
+  llvm::SpecificBumpPtrAllocator<T> Alloc;
+};
+
+template <typename T, typename... U> T *make(U &&... Args) {
+  static SpecificAlloc<T> Alloc;
+  return new (Alloc.Alloc.Allocate()) T(std::forward<U>(Args)...);
+}
+
+inline void freeArena() {
+  for (SpecificAllocBase *Alloc : SpecificAllocBase::Instances)
+    Alloc->reset();
+  BAlloc.Reset();
+}
+}
+}
+
+#endif
diff --git a/COFF/ModuleDef.cpp b/COFF/ModuleDef.cpp
index 5e393f45d184..a273b6f535db 100644
--- a/COFF/ModuleDef.cpp
+++ b/COFF/ModuleDef.cpp
@@ -18,6 +18,7 @@
 
 #include "Config.h"
 #include "Error.h"
+#include "Memory.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/StringSwitch.h"
 #include "llvm/Support/StringSaver.h"
@@ -113,7 +114,7 @@ private:
 
 class Parser {
 public:
-  explicit Parser(StringRef S, StringSaver *A) : Lex(S), Alloc(A) {}
+  explicit Parser(StringRef S) : Lex(S) {}
 
   void parse() {
     do {
@@ -197,9 +198,9 @@ private:
 
     if (Config->Machine == I386) {
       if (!isDecorated(E.Name))
-        E.Name = Alloc->save("_" + E.Name);
+        E.Name = Saver.save("_" + E.Name);
       if (!E.ExtName.empty() && !isDecorated(E.ExtName))
-        E.ExtName = Alloc->save("_" + E.ExtName);
+        E.ExtName = Saver.save("_" + E.ExtName);
     }
 
     for (;;) {
@@ -278,14 +279,11 @@ private:
   Lexer Lex;
   Token Tok;
   std::vector<Token> Stack;
-  StringSaver *Alloc;
 };
 
 } // anonymous namespace
 
-void parseModuleDefs(MemoryBufferRef MB, StringSaver *Alloc) {
-  Parser(MB.getBuffer(), Alloc).parse();
-}
+void parseModuleDefs(MemoryBufferRef MB) { Parser(MB.getBuffer()).parse(); }
 
 } // namespace coff
 } // namespace lld
diff --git a/COFF/Options.td b/COFF/Options.td
index e5c9c5b4635b..9dfbcc8e188c 100644
--- a/COFF/Options.td
+++ b/COFF/Options.td
@@ -27,6 +27,7 @@ def failifmismatch : P<"failifmismatch", "">;
 def heap    : P<"heap", "Size of the heap">;
 def implib  : P<"implib", "Import library name">;
 def libpath : P<"libpath", "Additional library search path">;
+def linkrepro : P<"linkrepro", "Dump linker invocation and input files for debugging">;
 def machine : P<"machine", "Specify target platform">;
 def merge   : P<"merge", "Combine sections">;
 def mllvm   : P<"mllvm", "Options to pass to LLVM">;
@@ -61,7 +62,9 @@ def deffile : Joined<["/", "-"], "def:">,
     HelpText<"Use module-definition file">;
 
 def debug : F<"debug">, HelpText<"Embed a symbol table in the image">;
+def debugtype : P<"debugtype", "Debug Info Options">;
 def dll : F<"dll">, HelpText<"Create a DLL">;
+def driver : P<"driver", "Generate a Windows NT Kernel Mode Driver">;
 def nodefaultlib_all : F<"nodefaultlib">;
 def noentry : F<"noentry">;
 def profile : F<"profile">;
@@ -91,7 +94,10 @@ def help_q : Flag<["/?", "-?"], "">, Alias<help>;
 def nosymtab : F<"nosymtab">;
 
 // Flags for debugging
-def lldmap : Joined<["/", "-"], "lldmap:">;
+def debugpdb : F<"debugpdb">;
+def dumppdb : Joined<["/", "-"], "dumppdb">;
+def lldmap : F<"lldmap">;
+def lldmap_file : Joined<["/", "-"], "lldmap:">;
 
 //==============================================================================
 // The flags below do nothing. They are defined only for link.exe compatibility.
diff --git a/COFF/PDB.cpp b/COFF/PDB.cpp
index 7606ccc680d3..56d5a3651143 100644
--- a/COFF/PDB.cpp
+++ b/COFF/PDB.cpp
@@ -7,55 +7,187 @@
 //
 //===----------------------------------------------------------------------===//
 
-#include "Driver.h"
+#include "PDB.h"
+#include "Chunks.h"
+#include "Config.h"
 #include "Error.h"
+#include "SymbolTable.h"
 #include "Symbols.h"
+#include "llvm/DebugInfo/CodeView/SymbolDumper.h"
+#include "llvm/DebugInfo/CodeView/TypeDumper.h"
+#include "llvm/DebugInfo/MSF/ByteStream.h"
+#include "llvm/DebugInfo/MSF/MSFBuilder.h"
+#include "llvm/DebugInfo/MSF/MSFCommon.h"
+#include "llvm/DebugInfo/PDB/Raw/DbiStream.h"
+#include "llvm/DebugInfo/PDB/Raw/DbiStreamBuilder.h"
+#include "llvm/DebugInfo/PDB/Raw/InfoStream.h"
+#include "llvm/DebugInfo/PDB/Raw/InfoStreamBuilder.h"
+#include "llvm/DebugInfo/PDB/Raw/PDBFile.h"
+#include "llvm/DebugInfo/PDB/Raw/PDBFileBuilder.h"
+#include "llvm/DebugInfo/PDB/Raw/TpiStream.h"
+#include "llvm/DebugInfo/PDB/Raw/TpiStreamBuilder.h"
+#include "llvm/Object/COFF.h"
 #include "llvm/Support/Endian.h"
 #include "llvm/Support/FileOutputBuffer.h"
+#include "llvm/Support/ScopedPrinter.h"
 #include <memory>
 
+using namespace lld;
+using namespace lld::coff;
 using namespace llvm;
+using namespace llvm::codeview;
 using namespace llvm::support;
 using namespace llvm::support::endian;
 
-const int PageSize = 4096;
-const uint8_t Magic[32] = "Microsoft C/C++ MSF 7.00\r\n\032DS\0\0";
-
-namespace {
-struct PDBHeader {
-  uint8_t Magic[32];
-  ulittle32_t PageSize;
-  ulittle32_t FpmPage;
-  ulittle32_t PageCount;
-  ulittle32_t RootSize;
-  ulittle32_t Reserved;
-  ulittle32_t RootPointer;
-};
-}
-
-void lld::coff::createPDB(StringRef Path) {
-  // Create a file.
-  size_t FileSize = PageSize * 3;
-  ErrorOr<std::unique_ptr<FileOutputBuffer>> BufferOrErr =
-      FileOutputBuffer::create(Path, FileSize);
-  if (auto EC = BufferOrErr.getError())
-    fatal(EC, "failed to open " + Path);
-  std::unique_ptr<FileOutputBuffer> Buffer = std::move(*BufferOrErr);
-
-  // Write the file header.
-  uint8_t *Buf = Buffer->getBufferStart();
-  auto *Hdr = reinterpret_cast<PDBHeader *>(Buf);
-  memcpy(Hdr->Magic, Magic, sizeof(Magic));
-  Hdr->PageSize = PageSize;
-  // I don't know what FpmPage field means, but it must not be 0.
-  Hdr->FpmPage = 1;
-  Hdr->PageCount = FileSize / PageSize;
-  // Root directory is empty, containing only the length field.
-  Hdr->RootSize = 4;
-  // Root directory is on page 1.
-  Hdr->RootPointer = 1;
-
-  // Write the root directory. Root stream is on page 2.
-  write32le(Buf + PageSize, 2);
-  Buffer->commit();
+using llvm::object::coff_section;
+
+static ExitOnError ExitOnErr;
+
+// Returns a list of all SectionChunks.
+static std::vector<coff_section> getInputSections(SymbolTable *Symtab) {
+  std::vector<coff_section> V;
+  for (Chunk *C : Symtab->getChunks())
+    if (auto *SC = dyn_cast<SectionChunk>(C))
+      V.push_back(*SC->Header);
+  return V;
+}
+
+static SectionChunk *findByName(std::vector<SectionChunk *> &Sections,
+                                StringRef Name) {
+  for (SectionChunk *C : Sections)
+    if (C->getSectionName() == Name)
+      return C;
+  return nullptr;
+}
+
+static ArrayRef<uint8_t> getDebugT(ObjectFile *File) {
+  SectionChunk *Sec = findByName(File->getDebugChunks(), ".debug$T");
+  if (!Sec)
+    return {};
+
+  // First 4 bytes are section magic.
+  ArrayRef<uint8_t> Data = Sec->getContents();
+  if (Data.size() < 4)
+    fatal(".debug$T too short");
+  if (read32le(Data.data()) != COFF::DEBUG_SECTION_MAGIC)
+    fatal(".debug$T has an invalid magic");
+  return Data.slice(4);
+}
+
+static void dumpDebugT(ScopedPrinter &W, ObjectFile *File) {
+  ArrayRef<uint8_t> Data = getDebugT(File);
+  if (Data.empty())
+    return;
+
+  msf::ByteStream Stream(Data);
+  CVTypeDumper TypeDumper(&W, false);
+  if (auto EC = TypeDumper.dump(Data))
+    fatal(EC, "CVTypeDumper::dump failed");
+}
+
+static void dumpDebugS(ScopedPrinter &W, ObjectFile *File) {
+  SectionChunk *Sec = findByName(File->getDebugChunks(), ".debug$S");
+  if (!Sec)
+    return;
+
+  msf::ByteStream Stream(Sec->getContents());
+  CVSymbolArray Symbols;
+  msf::StreamReader Reader(Stream);
+  if (auto EC = Reader.readArray(Symbols, Reader.getLength()))
+    fatal(EC, "StreamReader.readArray<CVSymbolArray> failed");
+
+  CVTypeDumper TypeDumper(&W, false);
+  CVSymbolDumper SymbolDumper(W, TypeDumper, nullptr, false);
+  if (auto EC = SymbolDumper.dump(Symbols))
+    fatal(EC, "CVSymbolDumper::dump failed");
+}
+
+// Dump CodeView debug info. This is for debugging.
+static void dumpCodeView(SymbolTable *Symtab) {
+  ScopedPrinter W(outs());
+
+  for (ObjectFile *File : Symtab->ObjectFiles) {
+    dumpDebugT(W, File);
+    dumpDebugS(W, File);
+  }
+}
+
+static void addTypeInfo(SymbolTable *Symtab,
+                        pdb::TpiStreamBuilder &TpiBuilder) {
+  for (ObjectFile *File : Symtab->ObjectFiles) {
+    ArrayRef<uint8_t> Data = getDebugT(File);
+    if (Data.empty())
+      continue;
+
+    msf::ByteStream Stream(Data);
+    codeview::CVTypeArray Records;
+    msf::StreamReader Reader(Stream);
+    if (auto EC = Reader.readArray(Records, Reader.getLength()))
+      fatal(EC, "Reader.readArray failed");
+    for (const codeview::CVType &Rec : Records)
+      TpiBuilder.addTypeRecord(Rec);
+  }
+}
+
+// Creates a PDB file.
+void coff::createPDB(StringRef Path, SymbolTable *Symtab,
+                     ArrayRef<uint8_t> SectionTable) {
+  if (Config->DumpPdb)
+    dumpCodeView(Symtab);
+
+  BumpPtrAllocator Alloc;
+  pdb::PDBFileBuilder Builder(Alloc);
+  ExitOnErr(Builder.initialize(4096)); // 4096 is blocksize
+
+  // Create streams in MSF for predefined streams, namely
+  // PDB, TPI, DBI and IPI.
+  for (int I = 0; I < (int)pdb::kSpecialStreamCount; ++I)
+    ExitOnErr(Builder.getMsfBuilder().addStream(0));
+
+  // Add an Info stream.
+  auto &InfoBuilder = Builder.getInfoBuilder();
+  InfoBuilder.setAge(1);
+
+  // Should be a random number, 0 for now.
+  InfoBuilder.setGuid({});
+
+  // Should be the current time, but set 0 for reproducibilty.
+  InfoBuilder.setSignature(0);
+  InfoBuilder.setVersion(pdb::PdbRaw_ImplVer::PdbImplVC70);
+
+  // Add an empty DPI stream.
+  auto &DbiBuilder = Builder.getDbiBuilder();
+  DbiBuilder.setVersionHeader(pdb::PdbDbiV110);
+
+  // Add an empty TPI stream.
+  auto &TpiBuilder = Builder.getTpiBuilder();
+  TpiBuilder.setVersionHeader(pdb::PdbTpiV80);
+  if (Config->DebugPdb)
+    addTypeInfo(Symtab, TpiBuilder);
+
+  // Add an empty IPI stream.
+  auto &IpiBuilder = Builder.getIpiBuilder();
+  IpiBuilder.setVersionHeader(pdb::PdbTpiV80);
+
+  // Add Section Contributions.
+  std::vector<pdb::SectionContrib> Contribs =
+      pdb::DbiStreamBuilder::createSectionContribs(getInputSections(Symtab));
+  DbiBuilder.setSectionContribs(Contribs);
+
+  // Add Section Map stream.
+  ArrayRef<object::coff_section> Sections = {
+      (const object::coff_section *)SectionTable.data(),
+      SectionTable.size() / sizeof(object::coff_section)};
+  std::vector<pdb::SecMapEntry> SectionMap =
+      pdb::DbiStreamBuilder::createSectionMap(Sections);
+  DbiBuilder.setSectionMap(SectionMap);
+
+  ExitOnErr(DbiBuilder.addModuleInfo("", "* Linker *"));
+
+  // Add COFF section header stream.
+  ExitOnErr(
+      DbiBuilder.addDbgStream(pdb::DbgHeaderType::SectionHdr, SectionTable));
+
+  // Write to a file.
+  ExitOnErr(Builder.commit(Path));
 }
diff --git a/COFF/PDB.h b/COFF/PDB.h
new file mode 100644
index 000000000000..091e90fa1ef1
--- /dev/null
+++ b/COFF/PDB.h
@@ -0,0 +1,25 @@
+//===- PDB.h ----------------------------------------------------*- C++ -*-===//
+//
+//                             The LLVM Linker
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLD_COFF_PDB_H
+#define LLD_COFF_PDB_H
+
+#include "llvm/ADT/ArrayRef.h"
+#include "llvm/ADT/StringRef.h"
+
+namespace lld {
+namespace coff {
+class SymbolTable;
+
+void createPDB(llvm::StringRef Path, SymbolTable *Symtab,
+               llvm::ArrayRef<uint8_t> SectionTable);
+}
+}
+
+#endif
diff --git a/COFF/Strings.cpp b/COFF/Strings.cpp
new file mode 100644
index 000000000000..d0558413f673
--- /dev/null
+++ b/COFF/Strings.cpp
@@ -0,0 +1,30 @@
+//===- Strings.cpp -------------------------------------------------------===//
+//
+//                             The LLVM Linker
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "Strings.h"
+
+#if defined(_MSC_VER)
+#include <Windows.h>
+#include <DbgHelp.h>
+#pragma comment(lib, "dbghelp.lib")
+#endif
+
+using namespace lld;
+using namespace lld::coff;
+using namespace llvm;
+
+Optional<std::string> coff::demangle(StringRef S) {
+#if defined(_MSC_VER)
+  char Buf[4096];
+  if (S.startswith("?"))
+    if (size_t Len = UnDecorateSymbolName(S.str().c_str(), Buf, sizeof(Buf), 0))
+      return std::string(Buf, Len);
+#endif
+  return None;
+}
diff --git a/COFF/Strings.h b/COFF/Strings.h
new file mode 100644
index 000000000000..1f85f3e2da5c
--- /dev/null
+++ b/COFF/Strings.h
@@ -0,0 +1,23 @@
+//===- Strings.h ------------------------------------------------*- C++ -*-===//
+//
+//                             The LLVM Linker
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLD_COFF_STRINGS_H
+#define LLD_COFF_STRINGS_H
+
+#include "llvm/ADT/Optional.h"
+#include "llvm/ADT/StringRef.h"
+#include <string>
+
+namespace lld {
+namespace coff {
+llvm::Optional<std::string> demangle(llvm::StringRef S);
+}
+}
+
+#endif
diff --git a/COFF/SymbolTable.cpp b/COFF/SymbolTable.cpp
index df9da4c36650..9cc0b75c1510 100644
--- a/COFF/SymbolTable.cpp
+++ b/COFF/SymbolTable.cpp
@@ -7,12 +7,12 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "SymbolTable.h"
 #include "Config.h"
 #include "Driver.h"
 #include "Error.h"
-#include "SymbolTable.h"
+#include "Memory.h"
 #include "Symbols.h"
-#include "lld/Core/Parallel.h"
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/LTO/legacy/LTOCodeGenerator.h"
 #include "llvm/Support/Debug.h"
@@ -24,222 +24,265 @@ using namespace llvm;
 namespace lld {
 namespace coff {
 
-void SymbolTable::addFile(std::unique_ptr<InputFile> FileP) {
-#if LLVM_ENABLE_THREADS
-  std::launch Policy = std::launch::async;
-#else
-  std::launch Policy = std::launch::deferred;
-#endif
+SymbolTable *Symtab;
 
-  InputFile *File = FileP.get();
-  Files.push_back(std::move(FileP));
-  if (auto *F = dyn_cast<ArchiveFile>(File)) {
-    ArchiveQueue.push_back(
-        std::async(Policy, [=]() { F->parse(); return F; }));
-    return;
+void SymbolTable::addFile(InputFile *File) {
+  if (Config->Verbose)
+    outs() << "Reading " << toString(File) << "\n";
+  File->parse();
+
+  MachineTypes MT = File->getMachineType();
+  if (Config->Machine == IMAGE_FILE_MACHINE_UNKNOWN) {
+    Config->Machine = MT;
+  } else if (MT != IMAGE_FILE_MACHINE_UNKNOWN && Config->Machine != MT) {
+    fatal(toString(File) + ": machine type " + machineToStr(MT) +
+          " conflicts with " + machineToStr(Config->Machine));
   }
-  ObjectQueue.push_back(
-      std::async(Policy, [=]() { File->parse(); return File; }));
+
   if (auto *F = dyn_cast<ObjectFile>(File)) {
     ObjectFiles.push_back(F);
   } else if (auto *F = dyn_cast<BitcodeFile>(File)) {
     BitcodeFiles.push_back(F);
-  } else {
-    ImportFiles.push_back(cast<ImportFile>(File));
+  } else if (auto *F = dyn_cast<ImportFile>(File)) {
+    ImportFiles.push_back(F);
   }
-}
 
-void SymbolTable::step() {
-  if (queueEmpty())
+  StringRef S = File->getDirectives();
+  if (S.empty())
     return;
-  readObjects();
-  readArchives();
-}
 
-void SymbolTable::run() {
-  while (!queueEmpty())
-    step();
-}
-
-void SymbolTable::readArchives() {
-  if (ArchiveQueue.empty())
-    return;
-
-  // Add lazy symbols to the symbol table. Lazy symbols that conflict
-  // with existing undefined symbols are accumulated in LazySyms.
-  std::vector<Symbol *> LazySyms;
-  for (std::future<ArchiveFile *> &Future : ArchiveQueue) {
-    ArchiveFile *File = Future.get();
-    if (Config->Verbose)
-      llvm::outs() << "Reading " << File->getShortName() << "\n";
-    for (Lazy &Sym : File->getLazySymbols())
-      addLazy(&Sym, &LazySyms);
-  }
-  ArchiveQueue.clear();
-
-  // Add archive member files to ObjectQueue that should resolve
-  // existing undefined symbols.
-  for (Symbol *Sym : LazySyms)
-    addMemberFile(cast<Lazy>(Sym->Body));
-}
-
-void SymbolTable::readObjects() {
-  if (ObjectQueue.empty())
-    return;
-
-  // Add defined and undefined symbols to the symbol table.
-  std::vector<StringRef> Directives;
-  for (size_t I = 0; I < ObjectQueue.size(); ++I) {
-    InputFile *File = ObjectQueue[I].get();
-    if (Config->Verbose)
-      llvm::outs() << "Reading " << File->getShortName() << "\n";
-    // Adding symbols may add more files to ObjectQueue
-    // (but not to ArchiveQueue).
-    for (SymbolBody *Sym : File->getSymbols())
-      if (Sym->isExternal())
-        addSymbol(Sym);
-    StringRef S = File->getDirectives();
-    if (!S.empty()) {
-      Directives.push_back(S);
-      if (Config->Verbose)
-        llvm::outs() << "Directives: " << File->getShortName()
-                     << ": " << S << "\n";
-    }
-  }
-  ObjectQueue.clear();
-
-  // Parse directive sections. This may add files to
-  // ArchiveQueue and ObjectQueue.
-  for (StringRef S : Directives)
-    Driver->parseDirectives(S);
-}
-
-bool SymbolTable::queueEmpty() {
-  return ArchiveQueue.empty() && ObjectQueue.empty();
+  if (Config->Verbose)
+    outs() << "Directives: " << toString(File) << ": " << S << "\n";
+  Driver->parseDirectives(S);
 }
 
-void SymbolTable::reportRemainingUndefines(bool Resolve) {
-  llvm::SmallPtrSet<SymbolBody *, 8> Undefs;
+void SymbolTable::reportRemainingUndefines() {
+  SmallPtrSet<SymbolBody *, 8> Undefs;
   for (auto &I : Symtab) {
     Symbol *Sym = I.second;
-    auto *Undef = dyn_cast<Undefined>(Sym->Body);
+    auto *Undef = dyn_cast<Undefined>(Sym->body());
     if (!Undef)
       continue;
+    if (!Sym->IsUsedInRegularObj)
+      continue;
     StringRef Name = Undef->getName();
     // A weak alias may have been resolved, so check for that.
     if (Defined *D = Undef->getWeakAlias()) {
-      if (Resolve)
-        Sym->Body = D;
+      // We resolve weak aliases by replacing the alias's SymbolBody with the
+      // target's SymbolBody. This causes all SymbolBody pointers referring to
+      // the old symbol to instead refer to the new symbol. However, we can't
+      // just blindly copy sizeof(Symbol::Body) bytes from D to Sym->Body
+      // because D may be an internal symbol, and internal symbols are stored as
+      // "unparented" SymbolBodies. For that reason we need to check which type
+      // of symbol we are dealing with and copy the correct number of bytes.
+      if (isa<DefinedRegular>(D))
+        memcpy(Sym->Body.buffer, D, sizeof(DefinedRegular));
+      else if (isa<DefinedAbsolute>(D))
+        memcpy(Sym->Body.buffer, D, sizeof(DefinedAbsolute));
+      else
+        // No other internal symbols are possible.
+        Sym->Body = D->symbol()->Body;
       continue;
     }
     // If we can resolve a symbol by removing __imp_ prefix, do that.
     // This odd rule is for compatibility with MSVC linker.
     if (Name.startswith("__imp_")) {
       Symbol *Imp = find(Name.substr(strlen("__imp_")));
-      if (Imp && isa<Defined>(Imp->Body)) {
-        if (!Resolve)
-          continue;
-        auto *D = cast<Defined>(Imp->Body);
-        auto *S = new (Alloc) DefinedLocalImport(Name, D);
-        LocalImportChunks.push_back(S->getChunk());
-        Sym->Body = S;
+      if (Imp && isa<Defined>(Imp->body())) {
+        auto *D = cast<Defined>(Imp->body());
+        replaceBody<DefinedLocalImport>(Sym, Name, D);
+        LocalImportChunks.push_back(
+            cast<DefinedLocalImport>(Sym->body())->getChunk());
         continue;
       }
     }
     // Remaining undefined symbols are not fatal if /force is specified.
     // They are replaced with dummy defined symbols.
-    if (Config->Force && Resolve)
-      Sym->Body = new (Alloc) DefinedAbsolute(Name, 0);
-    Undefs.insert(Sym->Body);
+    if (Config->Force)
+      replaceBody<DefinedAbsolute>(Sym, Name, 0);
+    Undefs.insert(Sym->body());
   }
   if (Undefs.empty())
     return;
-  for (Undefined *U : Config->GCRoot)
-    if (Undefs.count(U->repl()))
-      llvm::errs() << "<root>: undefined symbol: " << U->getName() << "\n";
-  for (std::unique_ptr<InputFile> &File : Files)
-    if (!isa<ArchiveFile>(File.get()))
-      for (SymbolBody *Sym : File->getSymbols())
-        if (Undefs.count(Sym->repl()))
-          llvm::errs() << File->getShortName() << ": undefined symbol: "
-                       << Sym->getName() << "\n";
+  for (SymbolBody *B : Config->GCRoot)
+    if (Undefs.count(B))
+      errs() << "<root>: undefined symbol: " << B->getName() << "\n";
+  for (ObjectFile *File : ObjectFiles)
+    for (SymbolBody *Sym : File->getSymbols())
+      if (Undefs.count(Sym))
+        errs() << toString(File) << ": undefined symbol: " << Sym->getName()
+               << "\n";
   if (!Config->Force)
     fatal("link failed");
 }
 
-void SymbolTable::addLazy(Lazy *New, std::vector<Symbol *> *Accum) {
-  Symbol *Sym = insert(New);
-  if (Sym->Body == New)
-    return;
-  SymbolBody *Existing = Sym->Body;
-  if (isa<Defined>(Existing))
-    return;
-  if (Lazy *L = dyn_cast<Lazy>(Existing))
-    if (L->getFileIndex() < New->getFileIndex())
-      return;
-  Sym->Body = New;
-  New->setBackref(Sym);
-  if (isa<Undefined>(Existing))
-    Accum->push_back(Sym);
+std::pair<Symbol *, bool> SymbolTable::insert(StringRef Name) {
+  Symbol *&Sym = Symtab[CachedHashStringRef(Name)];
+  if (Sym)
+    return {Sym, false};
+  Sym = make<Symbol>();
+  Sym->IsUsedInRegularObj = false;
+  Sym->PendingArchiveLoad = false;
+  return {Sym, true};
 }
 
-void SymbolTable::addSymbol(SymbolBody *New) {
-  // Find an existing symbol or create and insert a new one.
-  assert(isa<Defined>(New) || isa<Undefined>(New));
-  Symbol *Sym = insert(New);
-  if (Sym->Body == New)
-    return;
-  SymbolBody *Existing = Sym->Body;
-
-  // If we have an undefined symbol and a lazy symbol,
-  // let the lazy symbol to read a member file.
-  if (auto *L = dyn_cast<Lazy>(Existing)) {
-    // Undefined symbols with weak aliases need not to be resolved,
-    // since they would be replaced with weak aliases if they remain
-    // undefined.
-    if (auto *U = dyn_cast<Undefined>(New)) {
-      if (!U->WeakAlias) {
-        addMemberFile(L);
-        return;
-      }
+Symbol *SymbolTable::addUndefined(StringRef Name, InputFile *F,
+                                  bool IsWeakAlias) {
+  Symbol *S;
+  bool WasInserted;
+  std::tie(S, WasInserted) = insert(Name);
+  if (!F || !isa<BitcodeFile>(F))
+    S->IsUsedInRegularObj = true;
+  if (WasInserted || (isa<Lazy>(S->body()) && IsWeakAlias)) {
+    replaceBody<Undefined>(S, Name);
+    return S;
+  }
+  if (auto *L = dyn_cast<Lazy>(S->body())) {
+    if (!S->PendingArchiveLoad) {
+      S->PendingArchiveLoad = true;
+      L->File->addMember(&L->Sym);
     }
-    Sym->Body = New;
+  }
+  return S;
+}
+
+void SymbolTable::addLazy(ArchiveFile *F, const Archive::Symbol Sym) {
+  StringRef Name = Sym.getName();
+  Symbol *S;
+  bool WasInserted;
+  std::tie(S, WasInserted) = insert(Name);
+  if (WasInserted) {
+    replaceBody<Lazy>(S, F, Sym);
     return;
   }
+  auto *U = dyn_cast<Undefined>(S->body());
+  if (!U || U->WeakAlias || S->PendingArchiveLoad)
+    return;
+  S->PendingArchiveLoad = true;
+  F->addMember(&Sym);
+}
+
+void SymbolTable::reportDuplicate(Symbol *Existing, InputFile *NewFile) {
+  fatal("duplicate symbol: " + toString(*Existing->body()) + " in " +
+        toString(Existing->body()->getFile()) + " and in " +
+        (NewFile ? toString(NewFile) : "(internal)"));
+}
 
-  // compare() returns -1, 0, or 1 if the lhs symbol is less preferable,
-  // equivalent (conflicting), or more preferable, respectively.
-  int Comp = Existing->compare(New);
-  if (Comp == 0)
-    fatal("duplicate symbol: " + Existing->getDebugName() + " and " +
-          New->getDebugName());
-  if (Comp < 0)
-    Sym->Body = New;
+Symbol *SymbolTable::addAbsolute(StringRef N, COFFSymbolRef Sym) {
+  Symbol *S;
+  bool WasInserted;
+  std::tie(S, WasInserted) = insert(N);
+  S->IsUsedInRegularObj = true;
+  if (WasInserted || isa<Undefined>(S->body()) || isa<Lazy>(S->body()))
+    replaceBody<DefinedAbsolute>(S, N, Sym);
+  else if (!isa<DefinedCOFF>(S->body()))
+    reportDuplicate(S, nullptr);
+  return S;
 }
 
-Symbol *SymbolTable::insert(SymbolBody *New) {
-  Symbol *&Sym = Symtab[New->getName()];
-  if (Sym) {
-    New->setBackref(Sym);
-    return Sym;
+Symbol *SymbolTable::addAbsolute(StringRef N, uint64_t VA) {
+  Symbol *S;
+  bool WasInserted;
+  std::tie(S, WasInserted) = insert(N);
+  S->IsUsedInRegularObj = true;
+  if (WasInserted || isa<Undefined>(S->body()) || isa<Lazy>(S->body()))
+    replaceBody<DefinedAbsolute>(S, N, VA);
+  else if (!isa<DefinedCOFF>(S->body()))
+    reportDuplicate(S, nullptr);
+  return S;
+}
+
+Symbol *SymbolTable::addRelative(StringRef N, uint64_t VA) {
+  Symbol *S;
+  bool WasInserted;
+  std::tie(S, WasInserted) = insert(N);
+  S->IsUsedInRegularObj = true;
+  if (WasInserted || isa<Undefined>(S->body()) || isa<Lazy>(S->body()))
+    replaceBody<DefinedRelative>(S, N, VA);
+  else if (!isa<DefinedCOFF>(S->body()))
+    reportDuplicate(S, nullptr);
+  return S;
+}
+
+Symbol *SymbolTable::addRegular(ObjectFile *F, COFFSymbolRef Sym,
+                                SectionChunk *C) {
+  StringRef Name;
+  F->getCOFFObj()->getSymbolName(Sym, Name);
+  Symbol *S;
+  bool WasInserted;
+  std::tie(S, WasInserted) = insert(Name);
+  S->IsUsedInRegularObj = true;
+  if (WasInserted || isa<Undefined>(S->body()) || isa<Lazy>(S->body()))
+    replaceBody<DefinedRegular>(S, F, Sym, C);
+  else if (auto *R = dyn_cast<DefinedRegular>(S->body())) {
+    if (!C->isCOMDAT() || !R->isCOMDAT())
+      reportDuplicate(S, F);
+  } else if (auto *B = dyn_cast<DefinedBitcode>(S->body())) {
+    if (B->IsReplaceable)
+      replaceBody<DefinedRegular>(S, F, Sym, C);
+    else if (!C->isCOMDAT())
+      reportDuplicate(S, F);
+  } else
+    replaceBody<DefinedRegular>(S, F, Sym, C);
+  return S;
+}
+
+Symbol *SymbolTable::addBitcode(BitcodeFile *F, StringRef N, bool IsReplaceable) {
+  Symbol *S;
+  bool WasInserted;
+  std::tie(S, WasInserted) = insert(N);
+  if (WasInserted || isa<Undefined>(S->body()) || isa<Lazy>(S->body())) {
+    replaceBody<DefinedBitcode>(S, F, N, IsReplaceable);
+    return S;
   }
-  Sym = new (Alloc) Symbol(New);
-  New->setBackref(Sym);
-  return Sym;
+  if (isa<DefinedCommon>(S->body()))
+    return S;
+  if (IsReplaceable)
+    if (isa<DefinedRegular>(S->body()) || isa<DefinedBitcode>(S->body()))
+      return S;
+  reportDuplicate(S, F);
+  return S;
 }
 
-// Reads an archive member file pointed by a given symbol.
-void SymbolTable::addMemberFile(Lazy *Body) {
-  std::unique_ptr<InputFile> File = Body->getMember();
+Symbol *SymbolTable::addCommon(ObjectFile *F, COFFSymbolRef Sym,
+                               CommonChunk *C) {
+  StringRef Name;
+  F->getCOFFObj()->getSymbolName(Sym, Name);
+  Symbol *S;
+  bool WasInserted;
+  std::tie(S, WasInserted) = insert(Name);
+  S->IsUsedInRegularObj = true;
+  if (WasInserted || !isa<DefinedCOFF>(S->body()))
+    replaceBody<DefinedCommon>(S, F, Sym, C);
+  else if (auto *DC = dyn_cast<DefinedCommon>(S->body()))
+    if (Sym.getValue() > DC->getSize())
+      replaceBody<DefinedCommon>(S, F, Sym, C);
+  return S;
+}
 
-  // getMember returns an empty buffer if the member was already
-  // read from the library.
-  if (!File)
-    return;
-  if (Config->Verbose)
-    llvm::outs() << "Loaded " << File->getShortName() << " for "
-                 << Body->getName() << "\n";
-  addFile(std::move(File));
+Symbol *SymbolTable::addImportData(StringRef N, ImportFile *F) {
+  Symbol *S;
+  bool WasInserted;
+  std::tie(S, WasInserted) = insert(N);
+  S->IsUsedInRegularObj = true;
+  if (WasInserted || isa<Undefined>(S->body()) || isa<Lazy>(S->body()))
+    replaceBody<DefinedImportData>(S, N, F);
+  else if (!isa<DefinedCOFF>(S->body()))
+    reportDuplicate(S, nullptr);
+  return S;
+}
+
+Symbol *SymbolTable::addImportThunk(StringRef Name, DefinedImportData *ID,
+                                    uint16_t Machine) {
+  Symbol *S;
+  bool WasInserted;
+  std::tie(S, WasInserted) = insert(Name);
+  S->IsUsedInRegularObj = true;
+  if (WasInserted || isa<Undefined>(S->body()) || isa<Lazy>(S->body()))
+    replaceBody<DefinedImportThunk>(S, Name, ID, Machine);
+  else if (!isa<DefinedCOFF>(S->body()))
+    reportDuplicate(S, nullptr);
+  return S;
 }
 
 std::vector<Chunk *> SymbolTable::getChunks() {
@@ -252,7 +295,7 @@ std::vector<Chunk *> SymbolTable::getChunks() {
 }
 
 Symbol *SymbolTable::find(StringRef Name) {
-  auto It = Symtab.find(Name);
+  auto It = Symtab.find(CachedHashStringRef(Name));
   if (It == Symtab.end())
     return nullptr;
   return It->second;
@@ -266,7 +309,7 @@ Symbol *SymbolTable::findUnderscore(StringRef Name) {
 
 StringRef SymbolTable::findByPrefix(StringRef Prefix) {
   for (auto Pair : Symtab) {
-    StringRef Name = Pair.first;
+    StringRef Name = Pair.first.val();
     if (Name.startswith(Prefix))
       return Name;
   }
@@ -275,7 +318,7 @@ StringRef SymbolTable::findByPrefix(StringRef Prefix) {
 
 StringRef SymbolTable::findMangle(StringRef Name) {
   if (Symbol *Sym = find(Name))
-    if (!isa<Undefined>(Sym->Body))
+    if (!isa<Undefined>(Sym->body()))
       return Name;
   if (Config->Machine != I386)
     return findByPrefix(("?" + Name + "@@Y").str());
@@ -289,39 +332,22 @@ StringRef SymbolTable::findMangle(StringRef Name) {
   return findByPrefix(("?" + Name.substr(1) + "@@Y").str());
 }
 
-void SymbolTable::mangleMaybe(Undefined *U) {
-  if (U->WeakAlias)
-    return;
-  if (!isa<Undefined>(U->repl()))
+void SymbolTable::mangleMaybe(SymbolBody *B) {
+  auto *U = dyn_cast<Undefined>(B);
+  if (!U || U->WeakAlias)
     return;
   StringRef Alias = findMangle(U->getName());
   if (!Alias.empty())
     U->WeakAlias = addUndefined(Alias);
 }
 
-Undefined *SymbolTable::addUndefined(StringRef Name) {
-  auto *New = new (Alloc) Undefined(Name);
-  addSymbol(New);
-  if (auto *U = dyn_cast<Undefined>(New->repl()))
-    return U;
-  return New;
-}
-
-DefinedRelative *SymbolTable::addRelative(StringRef Name, uint64_t VA) {
-  auto *New = new (Alloc) DefinedRelative(Name, VA);
-  addSymbol(New);
-  return New;
-}
-
-DefinedAbsolute *SymbolTable::addAbsolute(StringRef Name, uint64_t VA) {
-  auto *New = new (Alloc) DefinedAbsolute(Name, VA);
-  addSymbol(New);
-  return New;
+SymbolBody *SymbolTable::addUndefined(StringRef Name) {
+  return addUndefined(Name, nullptr, false)->body();
 }
 
 void SymbolTable::printMap(llvm::raw_ostream &OS) {
   for (ObjectFile *File : ObjectFiles) {
-    OS << File->getShortName() << ":\n";
+    OS << toString(File) << ":\n";
     for (SymbolBody *Body : File->getSymbols())
       if (auto *R = dyn_cast<DefinedRegular>(Body))
         if (R->getChunk()->isLive())
@@ -330,84 +356,32 @@ void SymbolTable::printMap(llvm::raw_ostream &OS) {
   }
 }
 
-void SymbolTable::addCombinedLTOObject(ObjectFile *Obj) {
-  for (SymbolBody *Body : Obj->getSymbols()) {
-    if (!Body->isExternal())
-      continue;
-    // We should not see any new undefined symbols at this point, but we'll
-    // diagnose them later in reportRemainingUndefines().
-    StringRef Name = Body->getName();
-    Symbol *Sym = insert(Body);
-    SymbolBody *Existing = Sym->Body;
-
-    if (Existing == Body)
-      continue;
-
-    if (isa<DefinedBitcode>(Existing)) {
-      Sym->Body = Body;
-      continue;
-    }
-    if (auto *L = dyn_cast<Lazy>(Existing)) {
-      // We may see new references to runtime library symbols such as __chkstk
-      // here. These symbols must be wholly defined in non-bitcode files.
-      addMemberFile(L);
-      continue;
-    }
-
-    int Comp = Existing->compare(Body);
-    if (Comp == 0)
-      fatal("LTO: unexpected duplicate symbol: " + Name);
-    if (Comp < 0)
-      Sym->Body = Body;
-  }
-}
-
 void SymbolTable::addCombinedLTOObjects() {
   if (BitcodeFiles.empty())
     return;
 
-  // Diagnose any undefined symbols early, but do not resolve weak externals,
-  // as resolution breaks the invariant that each Symbol points to a unique
-  // SymbolBody, which we rely on to replace DefinedBitcode symbols correctly.
-  reportRemainingUndefines(/*Resolve=*/false);
-
   // Create an object file and add it to the symbol table by replacing any
   // DefinedBitcode symbols with the definitions in the object file.
   LTOCodeGenerator CG(BitcodeFile::Context);
   CG.setOptLevel(Config->LTOOptLevel);
-  std::vector<ObjectFile *> Objs = createLTOObjects(&CG);
-
-  for (ObjectFile *Obj : Objs)
-    addCombinedLTOObject(Obj);
-
-  size_t NumBitcodeFiles = BitcodeFiles.size();
-  run();
-  if (BitcodeFiles.size() != NumBitcodeFiles)
-    fatal("LTO: late loaded symbol created new bitcode reference");
+  for (ObjectFile *Obj : createLTOObjects(&CG))
+    Obj->parse();
 }
 
 // Combine and compile bitcode files and then return the result
 // as a vector of regular COFF object files.
 std::vector<ObjectFile *> SymbolTable::createLTOObjects(LTOCodeGenerator *CG) {
-  // All symbols referenced by non-bitcode objects must be preserved.
-  for (ObjectFile *File : ObjectFiles)
-    for (SymbolBody *Body : File->getSymbols())
-      if (auto *S = dyn_cast<DefinedBitcode>(Body->repl()))
-        CG->addMustPreserveSymbol(S->getName());
-
-  // Likewise for bitcode symbols which we initially resolved to non-bitcode.
+  // All symbols referenced by non-bitcode objects, including GC roots, must be
+  // preserved. We must also replace bitcode symbols with undefined symbols so
+  // that they may be replaced with real definitions without conflicting.
   for (BitcodeFile *File : BitcodeFiles)
-    for (SymbolBody *Body : File->getSymbols())
-      if (isa<DefinedBitcode>(Body) && !isa<DefinedBitcode>(Body->repl()))
+    for (SymbolBody *Body : File->getSymbols()) {
+      if (!isa<DefinedBitcode>(Body))
+        continue;
+      if (Body->symbol()->IsUsedInRegularObj)
         CG->addMustPreserveSymbol(Body->getName());
-
-  // Likewise for other symbols that must be preserved.
-  for (Undefined *U : Config->GCRoot) {
-    if (auto *S = dyn_cast<DefinedBitcode>(U->repl()))
-      CG->addMustPreserveSymbol(S->getName());
-    else if (auto *S = dyn_cast_or_null<DefinedBitcode>(U->getWeakAlias()))
-      CG->addMustPreserveSymbol(S->getName());
-  }
+      replaceBody<Undefined>(Body->symbol(), Body->getName());
+    }
 
   CG->setModule(BitcodeFiles[0]->takeModule());
   for (unsigned I = 1, E = BitcodeFiles.size(); I != E; ++I)
@@ -434,10 +408,8 @@ std::vector<ObjectFile *> SymbolTable::createLTOObjects(LTOCodeGenerator *CG) {
 
   std::vector<ObjectFile *> ObjFiles;
   for (SmallString<0> &Obj : Objs) {
-    auto *ObjFile = new ObjectFile(MemoryBufferRef(Obj, "<LTO object>"));
-    Files.emplace_back(ObjFile);
+    auto *ObjFile = make<ObjectFile>(MemoryBufferRef(Obj, "<LTO object>"));
     ObjectFiles.push_back(ObjFile);
-    ObjFile->parse();
     ObjFiles.push_back(ObjFile);
   }
 
diff --git a/COFF/SymbolTable.h b/COFF/SymbolTable.h
index 8bf4387cdfff..703821f2e124 100644
--- a/COFF/SymbolTable.h
+++ b/COFF/SymbolTable.h
@@ -11,18 +11,12 @@
 #define LLD_COFF_SYMBOL_TABLE_H
 
 #include "InputFiles.h"
+#include "llvm/ADT/CachedHashString.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/DenseMapInfo.h"
 #include "llvm/Support/Allocator.h"
 #include "llvm/Support/raw_ostream.h"
 
-#ifdef _MSC_VER
-// <future> depends on <eh.h> for __uncaught_exception.
-#include <eh.h>
-#endif
-
-#include <future>
-
 namespace llvm {
 struct LTOCodeGenerator;
 }
@@ -31,8 +25,12 @@ namespace lld {
 namespace coff {
 
 class Chunk;
+class CommonChunk;
 class Defined;
+class DefinedAbsolute;
+class DefinedRelative;
 class Lazy;
+class SectionChunk;
 class SymbolBody;
 struct Symbol;
 
@@ -45,18 +43,17 @@ struct Symbol;
 // conflicts. For example, obviously, a defined symbol is better than
 // an undefined symbol. Or, if there's a conflict between a lazy and a
 // undefined, it'll read an archive member to read a real definition
-// to replace the lazy symbol. The logic is implemented in resolve().
+// to replace the lazy symbol. The logic is implemented in the
+// add*() functions, which are called by input files as they are parsed.
+// There is one add* function per symbol type.
 class SymbolTable {
 public:
-  void addFile(std::unique_ptr<InputFile> File);
-  std::vector<std::unique_ptr<InputFile>> &getFiles() { return Files; }
-  void step();
-  void run();
-  bool queueEmpty();
+  void addFile(InputFile *File);
 
-  // Print an error message on undefined symbols. If Resolve is true, try to
-  // resolve any undefined symbols and update the symbol table accordingly.
-  void reportRemainingUndefines(bool Resolve);
+  // Try to resolve any undefined symbols and update the symbol table
+  // accordingly, then print an error message for any remaining undefined
+  // symbols.
+  void reportRemainingUndefines();
 
   // Returns a list of chunks of selected symbols.
   std::vector<Chunk *> getChunks();
@@ -69,7 +66,7 @@ public:
   // mangled symbol. This function tries to find a mangled name
   // for U from the symbol table, and if found, set the symbol as
   // a weak alias for U.
-  void mangleMaybe(Undefined *U);
+  void mangleMaybe(SymbolBody *B);
   StringRef findMangle(StringRef Name);
 
   // Print a layout map to OS.
@@ -88,37 +85,44 @@ public:
   std::vector<ObjectFile *> ObjectFiles;
 
   // Creates an Undefined symbol for a given name.
-  Undefined *addUndefined(StringRef Name);
-  DefinedRelative *addRelative(StringRef Name, uint64_t VA);
-  DefinedAbsolute *addAbsolute(StringRef Name, uint64_t VA);
+  SymbolBody *addUndefined(StringRef Name);
+
+  Symbol *addRelative(StringRef N, uint64_t VA);
+  Symbol *addAbsolute(StringRef N, uint64_t VA);
+
+  Symbol *addUndefined(StringRef Name, InputFile *F, bool IsWeakAlias);
+  void addLazy(ArchiveFile *F, const Archive::Symbol Sym);
+  Symbol *addAbsolute(StringRef N, COFFSymbolRef S);
+  Symbol *addRegular(ObjectFile *F, COFFSymbolRef S, SectionChunk *C);
+  Symbol *addBitcode(BitcodeFile *F, StringRef N, bool IsReplaceable);
+  Symbol *addCommon(ObjectFile *F, COFFSymbolRef S, CommonChunk *C);
+  Symbol *addImportData(StringRef N, ImportFile *F);
+  Symbol *addImportThunk(StringRef Name, DefinedImportData *S,
+                         uint16_t Machine);
+
+  void reportDuplicate(Symbol *Existing, InputFile *NewFile);
 
   // A list of chunks which to be added to .rdata.
   std::vector<Chunk *> LocalImportChunks;
 
 private:
-  void readArchives();
+  void readArchive();
   void readObjects();
 
-  void addSymbol(SymbolBody *New);
-  void addLazy(Lazy *New, std::vector<Symbol *> *Accum);
-  Symbol *insert(SymbolBody *New);
+  std::pair<Symbol *, bool> insert(StringRef Name);
   StringRef findByPrefix(StringRef Prefix);
 
-  void addMemberFile(Lazy *Body);
   void addCombinedLTOObject(ObjectFile *Obj);
   std::vector<ObjectFile *> createLTOObjects(llvm::LTOCodeGenerator *CG);
 
-  llvm::DenseMap<StringRef, Symbol *> Symtab;
-
-  std::vector<std::unique_ptr<InputFile>> Files;
-  std::vector<std::future<ArchiveFile *>> ArchiveQueue;
-  std::vector<std::future<InputFile *>> ObjectQueue;
+  llvm::DenseMap<llvm::CachedHashStringRef, Symbol *> Symtab;
 
   std::vector<BitcodeFile *> BitcodeFiles;
   std::vector<SmallString<0>> Objs;
-  llvm::BumpPtrAllocator Alloc;
 };
 
+extern SymbolTable *Symtab;
+
 } // namespace coff
 } // namespace lld
 
diff --git a/COFF/Symbols.cpp b/COFF/Symbols.cpp
index 6e2db6631ce7..6de85d581f49 100644
--- a/COFF/Symbols.cpp
+++ b/COFF/Symbols.cpp
@@ -7,16 +7,17 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "Symbols.h"
 #include "Error.h"
 #include "InputFiles.h"
-#include "Symbols.h"
+#include "Memory.h"
+#include "Strings.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
 
+using namespace llvm;
 using namespace llvm::object;
-using llvm::sys::fs::identify_magic;
-using llvm::sys::fs::file_magic;
 
 namespace lld {
 namespace coff {
@@ -36,130 +37,14 @@ StringRef SymbolBody::getName() {
   return Name;
 }
 
-// Returns 1, 0 or -1 if this symbol should take precedence
-// over the Other, tie or lose, respectively.
-int SymbolBody::compare(SymbolBody *Other) {
-  Kind LK = kind(), RK = Other->kind();
-
-  // Normalize so that the smaller kind is on the left.
-  if (LK > RK)
-    return -Other->compare(this);
-
-  // First handle comparisons between two different kinds.
-  if (LK != RK) {
-    if (RK > LastDefinedKind) {
-      if (LK == LazyKind && cast<Undefined>(Other)->WeakAlias)
-        return -1;
-
-      // The LHS is either defined or lazy and so it wins.
-      assert((LK <= LastDefinedKind || LK == LazyKind) && "Bad kind!");
-      return 1;
-    }
-
-    // Bitcode has special complexities.
-    if (RK == DefinedBitcodeKind) {
-      auto *RHS = cast<DefinedBitcode>(Other);
-
-      switch (LK) {
-      case DefinedCommonKind:
-        return 1;
-
-      case DefinedRegularKind:
-        // As an approximation, regular symbols win over bitcode symbols,
-        // but we definitely have a conflict if the regular symbol is not
-        // replaceable and neither is the bitcode symbol. We do not
-        // replicate the rest of the symbol resolution logic here; symbol
-        // resolution will be done accurately after lowering bitcode symbols
-        // to regular symbols in addCombinedLTOObject().
-        if (cast<DefinedRegular>(this)->isCOMDAT() || RHS->IsReplaceable)
-          return 1;
-
-        // Fallthrough to the default of a tie otherwise.
-      default:
-        return 0;
-      }
-    }
-
-    // Either of the object file kind will trump a higher kind.
-    if (LK <= LastDefinedCOFFKind)
-      return 1;
-
-    // The remaining kind pairs are ties amongst defined symbols.
-    return 0;
-  }
-
-  // Now handle the case where the kinds are the same.
-  switch (LK) {
-  case DefinedRegularKind: {
-    auto *LHS = cast<DefinedRegular>(this);
-    auto *RHS = cast<DefinedRegular>(Other);
-    if (LHS->isCOMDAT() && RHS->isCOMDAT())
-      return LHS->getFileIndex() < RHS->getFileIndex() ? 1 : -1;
-    return 0;
-  }
-
-  case DefinedCommonKind: {
-    auto *LHS = cast<DefinedCommon>(this);
-    auto *RHS = cast<DefinedCommon>(Other);
-    if (LHS->getSize() == RHS->getSize())
-      return LHS->getFileIndex() < RHS->getFileIndex() ? 1 : -1;
-    return LHS->getSize() > RHS->getSize() ? 1 : -1;
-  }
-
-  case DefinedBitcodeKind: {
-    auto *LHS = cast<DefinedBitcode>(this);
-    auto *RHS = cast<DefinedBitcode>(Other);
-    // If both are non-replaceable, we have a tie.
-    if (!LHS->IsReplaceable && !RHS->IsReplaceable)
-      return 0;
-
-    // Non-replaceable symbols win, but even two replaceable symboles don't
-    // tie. If both symbols are replaceable, choice is arbitrary.
-    if (RHS->IsReplaceable && LHS->IsReplaceable)
-      return uintptr_t(LHS) < uintptr_t(RHS) ? 1 : -1;
-    return LHS->IsReplaceable ? -1 : 1;
-  }
-
-  case LazyKind: {
-    // Don't tie, pick the earliest.
-    auto *LHS = cast<Lazy>(this);
-    auto *RHS = cast<Lazy>(Other);
-    return LHS->getFileIndex() < RHS->getFileIndex() ? 1 : -1;
-  }
-
-  case UndefinedKind: {
-    auto *LHS = cast<Undefined>(this);
-    auto *RHS = cast<Undefined>(Other);
-    // Tie if both undefined symbols have different weak aliases.
-    if (LHS->WeakAlias && RHS->WeakAlias) {
-      if (LHS->WeakAlias->getName() != RHS->WeakAlias->getName())
-        return 0;
-      return uintptr_t(LHS) < uintptr_t(RHS) ? 1 : -1;
-    }
-    return LHS->WeakAlias ? 1 : -1;
-  }
-
-  case DefinedLocalImportKind:
-  case DefinedImportThunkKind:
-  case DefinedImportDataKind:
-  case DefinedAbsoluteKind:
-  case DefinedRelativeKind:
-    // These all simply tie.
-    return 0;
-  }
-  llvm_unreachable("unknown symbol kind");
-}
-
-std::string SymbolBody::getDebugName() {
-  std::string N = getName().str();
-  if (auto *D = dyn_cast<DefinedCOFF>(this)) {
-    N += " ";
-    N += D->File->getShortName();
-  } else if (auto *D = dyn_cast<DefinedBitcode>(this)) {
-    N += " ";
-    N += D->File->getShortName();
-  }
-  return N;
+InputFile *SymbolBody::getFile() {
+  if (auto *Sym = dyn_cast<DefinedCOFF>(this))
+    return Sym->File;
+  if (auto *Sym = dyn_cast<DefinedBitcode>(this))
+    return Sym->File;
+  if (auto *Sym = dyn_cast<Lazy>(this))
+    return Sym->File;
+  return nullptr;
 }
 
 COFFSymbolRef DefinedCOFF::getCOFFSymbol() {
@@ -174,44 +59,27 @@ DefinedImportThunk::DefinedImportThunk(StringRef Name, DefinedImportData *S,
                                        uint16_t Machine)
     : Defined(DefinedImportThunkKind, Name) {
   switch (Machine) {
-  case AMD64: Data.reset(new ImportThunkChunkX64(S)); return;
-  case I386:  Data.reset(new ImportThunkChunkX86(S)); return;
-  case ARMNT: Data.reset(new ImportThunkChunkARM(S)); return;
+  case AMD64: Data = make<ImportThunkChunkX64>(S); return;
+  case I386:  Data = make<ImportThunkChunkX86>(S); return;
+  case ARMNT: Data = make<ImportThunkChunkARM>(S); return;
   default:    llvm_unreachable("unknown machine type");
   }
 }
 
-std::unique_ptr<InputFile> Lazy::getMember() {
-  MemoryBufferRef MBRef = File->getMember(&Sym);
-
-  // getMember returns an empty buffer if the member was already
-  // read from the library.
-  if (MBRef.getBuffer().empty())
-    return std::unique_ptr<InputFile>(nullptr);
-
-  file_magic Magic = identify_magic(MBRef.getBuffer());
-  if (Magic == file_magic::coff_import_library)
-    return std::unique_ptr<InputFile>(new ImportFile(MBRef));
-
-  std::unique_ptr<InputFile> Obj;
-  if (Magic == file_magic::coff_object)
-    Obj.reset(new ObjectFile(MBRef));
-  else if (Magic == file_magic::bitcode)
-    Obj.reset(new BitcodeFile(MBRef));
-  else
-    fatal("unknown file type: " + File->getName());
-
-  Obj->setParentName(File->getName());
-  return Obj;
-}
-
 Defined *Undefined::getWeakAlias() {
   // A weak alias may be a weak alias to another symbol, so check recursively.
   for (SymbolBody *A = WeakAlias; A; A = cast<Undefined>(A)->WeakAlias)
-    if (auto *D = dyn_cast<Defined>(A->repl()))
+    if (auto *D = dyn_cast<Defined>(A))
       return D;
   return nullptr;
 }
 
+// Returns a symbol name for an error message.
+std::string toString(SymbolBody &B) {
+  if (Optional<std::string> S = demangle(B.getName()))
+    return ("\"" + *S + "\" (" + B.getName() + ")").str();
+  return B.getName();
+}
+
 } // namespace coff
 } // namespace lld
diff --git a/COFF/Symbols.h b/COFF/Symbols.h
index f96c1fb3cc1d..bc9ad4aa8aff 100644
--- a/COFF/Symbols.h
+++ b/COFF/Symbols.h
@@ -12,6 +12,7 @@
 
 #include "Chunks.h"
 #include "Config.h"
+#include "Memory.h"
 #include "lld/Core/LLVM.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/Object/Archive.h"
@@ -32,15 +33,8 @@ class ArchiveFile;
 class BitcodeFile;
 class InputFile;
 class ObjectFile;
-class SymbolBody;
-
-// A real symbol object, SymbolBody, is usually accessed indirectly
-// through a Symbol. There's always one Symbol for each symbol name.
-// The resolver updates SymbolBody pointers as it resolves symbols.
-struct Symbol {
-  explicit Symbol(SymbolBody *P) : Body(P) {}
-  SymbolBody *Body;
-};
+struct Symbol;
+class SymbolTable;
 
 // The base class for real symbol classes.
 class SymbolBody {
@@ -75,28 +69,19 @@ public:
   // Returns the symbol name.
   StringRef getName();
 
-  // A SymbolBody has a backreference to a Symbol. Originally they are
-  // doubly-linked. A backreference will never change. But the pointer
-  // in the Symbol may be mutated by the resolver. If you have a
-  // pointer P to a SymbolBody and are not sure whether the resolver
-  // has chosen the object among other objects having the same name,
-  // you can access P->Backref->Body to get the resolver's result.
-  void setBackref(Symbol *P) { Backref = P; }
-  SymbolBody *repl() { return Backref ? Backref->Body : this; }
-
-  // Decides which symbol should "win" in the symbol table, this or
-  // the Other. Returns 1 if this wins, -1 if the Other wins, or 0 if
-  // they are duplicate (conflicting) symbols.
-  int compare(SymbolBody *Other);
+  // Returns the file from which this symbol was created.
+  InputFile *getFile();
 
-  // Returns a name of this symbol including source file name.
-  // Used only for debugging and logging.
-  std::string getDebugName();
+  Symbol *symbol();
+  const Symbol *symbol() const {
+    return const_cast<SymbolBody *>(this)->symbol();
+  }
 
 protected:
+  friend SymbolTable;
   explicit SymbolBody(Kind K, StringRef N = "")
       : SymbolKind(K), IsExternal(true), IsCOMDAT(false),
-        IsReplaceable(false), Name(N) {}
+        IsReplaceable(false), WrittenToSymtab(false), Name(N) {}
 
   const unsigned SymbolKind : 8;
   unsigned IsExternal : 1;
@@ -107,8 +92,12 @@ protected:
   // This bit is used by the \c DefinedBitcode subclass.
   unsigned IsReplaceable : 1;
 
+public:
+  // This bit is used by Writer::createSymbolAndStringTable().
+  unsigned WrittenToSymtab : 1;
+
+protected:
   StringRef Name;
-  Symbol *Backref = nullptr;
 };
 
 // The base class for any defined symbols, including absolute symbols,
@@ -149,12 +138,13 @@ public:
     return S->kind() <= LastDefinedCOFFKind;
   }
 
-  int getFileIndex() { return File->Index; }
+  ObjectFile *getFile() { return File; }
 
   COFFSymbolRef getCOFFSymbol();
 
-protected:
   ObjectFile *File;
+
+protected:
   const coff_symbol_generic *Sym;
 };
 
@@ -194,7 +184,7 @@ public:
   uint64_t getRVA() { return Data->getRVA(); }
 
 private:
-  friend SymbolBody;
+  friend SymbolTable;
   uint64_t getSize() { return Sym->Value; }
   CommonChunk *Data;
 };
@@ -253,14 +243,12 @@ public:
 
   static bool classof(const SymbolBody *S) { return S->kind() == LazyKind; }
 
-  // Returns an object file for this symbol, or a nullptr if the file
-  // was already returned.
-  std::unique_ptr<InputFile> getMember();
+  ArchiveFile *File;
 
-  int getFileIndex() { return File->Index; }
+private:
+  friend SymbolTable;
 
 private:
-  ArchiveFile *File;
   const Archive::Symbol Sym;
 };
 
@@ -293,26 +281,22 @@ public:
 // table in an output. The former has "__imp_" prefix.
 class DefinedImportData : public Defined {
 public:
-  DefinedImportData(StringRef D, StringRef N, StringRef E,
-                    const coff_import_header *H)
-      : Defined(DefinedImportDataKind, N), DLLName(D), ExternalName(E), Hdr(H) {
+  DefinedImportData(StringRef N, ImportFile *F)
+      : Defined(DefinedImportDataKind, N), File(F) {
   }
 
   static bool classof(const SymbolBody *S) {
     return S->kind() == DefinedImportDataKind;
   }
 
-  uint64_t getRVA() { return Location->getRVA(); }
-  StringRef getDLLName() { return DLLName; }
-  StringRef getExternalName() { return ExternalName; }
-  void setLocation(Chunk *AddressTable) { Location = AddressTable; }
-  uint16_t getOrdinal() { return Hdr->OrdinalHint; }
+  uint64_t getRVA() { return File->Location->getRVA(); }
+  StringRef getDLLName() { return File->DLLName; }
+  StringRef getExternalName() { return File->ExternalName; }
+  void setLocation(Chunk *AddressTable) { File->Location = AddressTable; }
+  uint16_t getOrdinal() { return File->Hdr->OrdinalHint; }
 
 private:
-  StringRef DLLName;
-  StringRef ExternalName;
-  const coff_import_header *Hdr;
-  Chunk *Location = nullptr;
+  ImportFile *File;
 };
 
 // This class represents a symbol for a jump table entry which jumps
@@ -329,10 +313,10 @@ public:
   }
 
   uint64_t getRVA() { return Data->getRVA(); }
-  Chunk *getChunk() { return Data.get(); }
+  Chunk *getChunk() { return Data; }
 
 private:
-  std::unique_ptr<Chunk> Data;
+  Chunk *Data;
 };
 
 // If you have a symbol "__imp_foo" in your object file, a symbol name
@@ -343,17 +327,17 @@ private:
 class DefinedLocalImport : public Defined {
 public:
   DefinedLocalImport(StringRef N, Defined *S)
-      : Defined(DefinedLocalImportKind, N), Data(S) {}
+      : Defined(DefinedLocalImportKind, N), Data(make<LocalImportChunk>(S)) {}
 
   static bool classof(const SymbolBody *S) {
     return S->kind() == DefinedLocalImportKind;
   }
 
-  uint64_t getRVA() { return Data.getRVA(); }
-  Chunk *getChunk() { return &Data; }
+  uint64_t getRVA() { return Data->getRVA(); }
+  Chunk *getChunk() { return Data; }
 
 private:
-  LocalImportChunk Data;
+  LocalImportChunk *Data;
 };
 
 class DefinedBitcode : public Defined {
@@ -361,6 +345,11 @@ class DefinedBitcode : public Defined {
 public:
   DefinedBitcode(BitcodeFile *F, StringRef N, bool IsReplaceable)
       : Defined(DefinedBitcodeKind, N), File(F) {
+    // IsReplaceable tracks whether the bitcode symbol may be replaced with some
+    // other (defined, common or bitcode) symbol. This is the case for common,
+    // comdat and weak external symbols. We try to replace bitcode symbols with
+    // "real" symbols (see SymbolTable::add{Regular,Bitcode}), and resolve the
+    // result against the real symbol from the combined LTO object.
     this->IsReplaceable = IsReplaceable;
   }
 
@@ -368,7 +357,6 @@ public:
     return S->kind() == DefinedBitcodeKind;
   }
 
-private:
   BitcodeFile *File;
 };
 
@@ -397,6 +385,52 @@ inline uint64_t Defined::getRVA() {
   llvm_unreachable("unknown symbol kind");
 }
 
+// A real symbol object, SymbolBody, is usually stored within a Symbol. There's
+// always one Symbol for each symbol name. The resolver updates the SymbolBody
+// stored in the Body field of this object as it resolves symbols. Symbol also
+// holds computed properties of symbol names.
+struct Symbol {
+  // True if this symbol was referenced by a regular (non-bitcode) object.
+  unsigned IsUsedInRegularObj : 1;
+
+  // True if we've seen both a lazy and an undefined symbol with this symbol
+  // name, which means that we have enqueued an archive member load and should
+  // not load any more archive members to resolve the same symbol.
+  unsigned PendingArchiveLoad : 1;
+
+  // This field is used to store the Symbol's SymbolBody. This instantiation of
+  // AlignedCharArrayUnion gives us a struct with a char array field that is
+  // large and aligned enough to store any derived class of SymbolBody.
+  llvm::AlignedCharArrayUnion<DefinedRegular, DefinedCommon, DefinedAbsolute,
+                              DefinedRelative, Lazy, Undefined,
+                              DefinedImportData, DefinedImportThunk,
+                              DefinedLocalImport, DefinedBitcode>
+      Body;
+
+  SymbolBody *body() {
+    return reinterpret_cast<SymbolBody *>(Body.buffer);
+  }
+  const SymbolBody *body() const { return const_cast<Symbol *>(this)->body(); }
+};
+
+template <typename T, typename... ArgT>
+void replaceBody(Symbol *S, ArgT &&... Arg) {
+  static_assert(sizeof(T) <= sizeof(S->Body), "Body too small");
+  static_assert(alignof(T) <= alignof(decltype(S->Body)),
+                "Body not aligned enough");
+  assert(static_cast<SymbolBody *>(static_cast<T *>(nullptr)) == nullptr &&
+         "Not a SymbolBody");
+  new (S->Body.buffer) T(std::forward<ArgT>(Arg)...);
+}
+
+inline Symbol *SymbolBody::symbol() {
+  assert(isExternal());
+  return reinterpret_cast<Symbol *>(reinterpret_cast<char *>(this) -
+                                    offsetof(Symbol, Body));
+}
+
+std::string toString(SymbolBody &B);
+
 } // namespace coff
 } // namespace lld
 
diff --git a/COFF/Writer.cpp b/COFF/Writer.cpp
index d8077df95701..3e69aebbb424 100644
--- a/COFF/Writer.cpp
+++ b/COFF/Writer.cpp
@@ -7,13 +7,15 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "Writer.h"
 #include "Config.h"
 #include "DLL.h"
 #include "Error.h"
 #include "InputFiles.h"
+#include "Memory.h"
+#include "PDB.h"
 #include "SymbolTable.h"
 #include "Symbols.h"
-#include "Writer.h"
 #include "lld/Core/Parallel.h"
 #include "llvm/ADT/DenseMap.h"
 #include "llvm/ADT/STLExtras.h"
@@ -21,6 +23,7 @@
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/Endian.h"
 #include "llvm/Support/FileOutputBuffer.h"
+#include "llvm/Support/RandomNumberGenerator.h"
 #include "llvm/Support/raw_ostream.h"
 #include <algorithm>
 #include <cstdio>
@@ -42,6 +45,61 @@ static const int DOSStubSize = 64;
 static const int NumberfOfDataDirectory = 16;
 
 namespace {
+
+class DebugDirectoryChunk : public Chunk {
+public:
+  DebugDirectoryChunk(const std::vector<std::unique_ptr<Chunk>> &R)
+      : Records(R) {}
+
+  size_t getSize() const override {
+    return Records.size() * sizeof(debug_directory);
+  }
+
+  void writeTo(uint8_t *B) const override {
+    auto *D = reinterpret_cast<debug_directory *>(B + OutputSectionOff);
+
+    for (const std::unique_ptr<Chunk> &Record : Records) {
+      D->Characteristics = 0;
+      D->TimeDateStamp = 0;
+      D->MajorVersion = 0;
+      D->MinorVersion = 0;
+      D->Type = COFF::IMAGE_DEBUG_TYPE_CODEVIEW;
+      D->SizeOfData = Record->getSize();
+      D->AddressOfRawData = Record->getRVA();
+      // TODO(compnerd) get the file offset
+      D->PointerToRawData = 0;
+
+      ++D;
+    }
+  }
+
+private:
+  const std::vector<std::unique_ptr<Chunk>> &Records;
+};
+
+class CVDebugRecordChunk : public Chunk {
+  size_t getSize() const override {
+    return sizeof(codeview::DebugInfo) + Config->PDBPath.size() + 1;
+  }
+
+  void writeTo(uint8_t *B) const override {
+    // Save off the DebugInfo entry to backfill the file signature (build id)
+    // in Writer::writeBuildId
+    DI = reinterpret_cast<codeview::DebugInfo *>(B + OutputSectionOff);
+
+    DI->Signature.CVSignature = OMF::Signature::PDB70;
+
+    // variable sized field (PDB Path)
+    auto *P = reinterpret_cast<char *>(B + OutputSectionOff + sizeof(*DI));
+    if (!Config->PDBPath.empty())
+      memcpy(P, Config->PDBPath.data(), Config->PDBPath.size());
+    P[Config->PDBPath.size()] = '\0';
+  }
+
+public:
+  mutable codeview::DebugInfo *DI = nullptr;
+};
+
 // The writer writes a SymbolTable result to a file.
 class Writer {
 public:
@@ -62,6 +120,7 @@ private:
   void setSectionPermissions();
   void writeSections();
   void sortExceptionTable();
+  void writeBuildId();
   void applyRelocations();
 
   llvm::Optional<coff_symbol16> createSymbol(Defined *D);
@@ -76,9 +135,7 @@ private:
   std::map<StringRef, std::vector<DefinedImportData *>> binImports();
 
   SymbolTable *Symtab;
-  std::unique_ptr<llvm::FileOutputBuffer> Buffer;
-  llvm::SpecificBumpPtrAllocator<OutputSection> CAlloc;
-  llvm::SpecificBumpPtrAllocator<BaserelChunk> BAlloc;
+  std::unique_ptr<FileOutputBuffer> Buffer;
   std::vector<OutputSection *> OutputSections;
   std::vector<char> Strtab;
   std::vector<llvm::object::coff_symbol16> OutputSymtab;
@@ -87,6 +144,11 @@ private:
   EdataContents Edata;
   std::unique_ptr<SEHTableChunk> SEHTable;
 
+  std::unique_ptr<Chunk> DebugDirectory;
+  std::vector<std::unique_ptr<Chunk>> DebugRecords;
+  CVDebugRecordChunk *BuildId = nullptr;
+  ArrayRef<uint8_t> SectionTable;
+
   uint64_t FileSize;
   uint32_t PointerToSymbolTable = 0;
   uint64_t SizeOfImage;
@@ -239,6 +301,11 @@ void Writer::run() {
   fixSafeSEHSymbols();
   writeSections();
   sortExceptionTable();
+  writeBuildId();
+
+  if (!Config->PDBPath.empty())
+    createPDB(Config->PDBPath, Symtab, SectionTable);
+
   if (auto EC = Buffer->commit())
     fatal(EC, "failed to write the output file");
 }
@@ -274,7 +341,7 @@ void Writer::createSections() {
     StringRef Name = getOutputSection(Pair.first);
     OutputSection *&Sec = Sections[Name];
     if (!Sec) {
-      Sec = new (CAlloc.Allocate()) OutputSection(Name);
+      Sec = make<OutputSection>(Name);
       OutputSections.push_back(Sec);
     }
     std::vector<Chunk *> &Chunks = Pair.second;
@@ -286,25 +353,46 @@ void Writer::createSections() {
 }
 
 void Writer::createMiscChunks() {
+  OutputSection *RData = createSection(".rdata");
+
   // Create thunks for locally-dllimported symbols.
   if (!Symtab->LocalImportChunks.empty()) {
-    OutputSection *Sec = createSection(".rdata");
     for (Chunk *C : Symtab->LocalImportChunks)
-      Sec->addChunk(C);
+      RData->addChunk(C);
+  }
+
+  // Create Debug Information Chunks
+  if (Config->Debug) {
+    DebugDirectory = llvm::make_unique<DebugDirectoryChunk>(DebugRecords);
+
+    // TODO(compnerd) create a coffgrp entry if DebugType::CV is not enabled
+    if (Config->DebugTypes & static_cast<unsigned>(coff::DebugType::CV)) {
+      auto Chunk = llvm::make_unique<CVDebugRecordChunk>();
+
+      BuildId = Chunk.get();
+      DebugRecords.push_back(std::move(Chunk));
+    }
+
+    RData->addChunk(DebugDirectory.get());
+    for (const std::unique_ptr<Chunk> &C : DebugRecords)
+      RData->addChunk(C.get());
   }
 
   // Create SEH table. x86-only.
   if (Config->Machine != I386)
     return;
+
   std::set<Defined *> Handlers;
+
   for (lld::coff::ObjectFile *File : Symtab->ObjectFiles) {
     if (!File->SEHCompat)
       return;
     for (SymbolBody *B : File->SEHandlers)
-      Handlers.insert(cast<Defined>(B->repl()));
+      Handlers.insert(cast<Defined>(B));
   }
+
   SEHTable.reset(new SEHTableChunk(Handlers));
-  createSection(".rdata")->addChunk(SEHTable.get());
+  RData->addChunk(SEHTable.get());
 }
 
 // Create .idata section for the DLL-imported symbol table.
@@ -340,7 +428,7 @@ void Writer::createImportTables() {
       Sec->addChunk(C);
   }
   if (!DelayIdata.empty()) {
-    Defined *Helper = cast<Defined>(Config->DelayLoadHelper->repl());
+    Defined *Helper = cast<Defined>(Config->DelayLoadHelper);
     DelayIdata.create(Helper);
     OutputSection *Sec = createSection(".didat");
     for (Chunk *C : DelayIdata.getChunks())
@@ -383,6 +471,10 @@ size_t Writer::addEntryToStringTable(StringRef Str) {
 }
 
 Optional<coff_symbol16> Writer::createSymbol(Defined *Def) {
+  // Relative symbols are unrepresentable in a COFF symbol table.
+  if (isa<DefinedRelative>(Def))
+    return None;
+
   if (auto *D = dyn_cast<DefinedRegular>(Def))
     if (!D->getChunk()->isLive())
       return None;
@@ -409,7 +501,6 @@ Optional<coff_symbol16> Writer::createSymbol(Defined *Def) {
 
   switch (Def->kind()) {
   case SymbolBody::DefinedAbsoluteKind:
-  case SymbolBody::DefinedRelativeKind:
     Sym.Value = Def->getRVA();
     Sym.SectionNumber = IMAGE_SYM_ABSOLUTE;
     break;
@@ -445,13 +536,11 @@ void Writer::createSymbolAndStringTable() {
   for (lld::coff::ObjectFile *File : Symtab->ObjectFiles)
     for (SymbolBody *B : File->getSymbols())
       if (auto *D = dyn_cast<Defined>(B))
-        if (Optional<coff_symbol16> Sym = createSymbol(D))
-          OutputSymtab.push_back(*Sym);
-
-  for (ImportFile *File : Symtab->ImportFiles)
-    for (SymbolBody *B : File->getSymbols())
-      if (Optional<coff_symbol16> Sym = createSymbol(cast<Defined>(B)))
-        OutputSymtab.push_back(*Sym);
+        if (!D->WrittenToSymtab) {
+          D->WrittenToSymtab = true;
+          if (Optional<coff_symbol16> Sym = createSymbol(D))
+            OutputSymtab.push_back(*Sym);
+        }
 
   OutputSection *LastSection = OutputSections.back();
   // We position the symbol table to be adjacent to the end of the last section.
@@ -542,7 +631,7 @@ template <typename PEHeaderTy> void Writer::writeHeader() {
   PE->SizeOfImage = SizeOfImage;
   PE->SizeOfHeaders = SizeOfHeaders;
   if (!Config->NoEntry) {
-    Defined *Entry = cast<Defined>(Config->Entry->repl());
+    Defined *Entry = cast<Defined>(Config->Entry);
     PE->AddressOfEntryPoint = Entry->getRVA();
     // Pointer to thumb code must have the LSB set, so adjust it.
     if (Config->Machine == ARMNT)
@@ -584,33 +673,32 @@ template <typename PEHeaderTy> void Writer::writeHeader() {
     Dir[IAT].RelativeVirtualAddress = Idata.getIATRVA();
     Dir[IAT].Size = Idata.getIATSize();
   }
-  if (!DelayIdata.empty()) {
-    Dir[DELAY_IMPORT_DESCRIPTOR].RelativeVirtualAddress =
-        DelayIdata.getDirRVA();
-    Dir[DELAY_IMPORT_DESCRIPTOR].Size = DelayIdata.getDirSize();
-  }
   if (OutputSection *Sec = findSection(".rsrc")) {
     Dir[RESOURCE_TABLE].RelativeVirtualAddress = Sec->getRVA();
     Dir[RESOURCE_TABLE].Size = Sec->getVirtualSize();
   }
-  if (OutputSection *Sec = findSection(".reloc")) {
-    Dir[BASE_RELOCATION_TABLE].RelativeVirtualAddress = Sec->getRVA();
-    Dir[BASE_RELOCATION_TABLE].Size = Sec->getVirtualSize();
-  }
   if (OutputSection *Sec = findSection(".pdata")) {
     Dir[EXCEPTION_TABLE].RelativeVirtualAddress = Sec->getRVA();
     Dir[EXCEPTION_TABLE].Size = Sec->getVirtualSize();
   }
+  if (OutputSection *Sec = findSection(".reloc")) {
+    Dir[BASE_RELOCATION_TABLE].RelativeVirtualAddress = Sec->getRVA();
+    Dir[BASE_RELOCATION_TABLE].Size = Sec->getVirtualSize();
+  }
   if (Symbol *Sym = Symtab->findUnderscore("_tls_used")) {
-    if (Defined *B = dyn_cast<Defined>(Sym->Body)) {
+    if (Defined *B = dyn_cast<Defined>(Sym->body())) {
       Dir[TLS_TABLE].RelativeVirtualAddress = B->getRVA();
       Dir[TLS_TABLE].Size = Config->is64()
                                 ? sizeof(object::coff_tls_directory64)
                                 : sizeof(object::coff_tls_directory32);
     }
   }
+  if (Config->Debug) {
+    Dir[DEBUG_DIRECTORY].RelativeVirtualAddress = DebugDirectory->getRVA();
+    Dir[DEBUG_DIRECTORY].Size = DebugDirectory->getSize();
+  }
   if (Symbol *Sym = Symtab->findUnderscore("_load_config_used")) {
-    if (auto *B = dyn_cast<DefinedRegular>(Sym->Body)) {
+    if (auto *B = dyn_cast<DefinedRegular>(Sym->body())) {
       SectionChunk *SC = B->getChunk();
       assert(B->getRVA() >= SC->getRVA());
       uint64_t OffsetInChunk = B->getRVA() - SC->getRVA();
@@ -626,12 +714,19 @@ template <typename PEHeaderTy> void Writer::writeHeader() {
       Dir[LOAD_CONFIG_TABLE].Size = LoadConfigSize;
     }
   }
+  if (!DelayIdata.empty()) {
+    Dir[DELAY_IMPORT_DESCRIPTOR].RelativeVirtualAddress =
+        DelayIdata.getDirRVA();
+    Dir[DELAY_IMPORT_DESCRIPTOR].Size = DelayIdata.getDirSize();
+  }
 
   // Write section table
   for (OutputSection *Sec : OutputSections) {
     Sec->writeHeaderTo(Buf);
     Buf += sizeof(coff_section);
   }
+  SectionTable = ArrayRef<uint8_t>(
+      Buf - OutputSections.size() * sizeof(coff_section), Buf);
 
   if (OutputSymtab.empty())
     return;
@@ -660,8 +755,10 @@ void Writer::openFile(StringRef Path) {
 void Writer::fixSafeSEHSymbols() {
   if (!SEHTable)
     return;
-  Config->SEHTable->setRVA(SEHTable->getRVA());
-  Config->SEHCount->setVA(SEHTable->getSize() / 4);
+  if (auto *T = dyn_cast<DefinedRelative>(Config->SEHTable->body()))
+    T->setRVA(SEHTable->getRVA());
+  if (auto *C = dyn_cast<DefinedAbsolute>(Config->SEHCount->body()))
+    C->setVA(SEHTable->getSize() / 4);
 }
 
 // Handles /section options to allow users to overwrite
@@ -715,6 +812,30 @@ void Writer::sortExceptionTable() {
   errs() << "warning: don't know how to handle .pdata.\n";
 }
 
+// Backfill the CVSignature in a PDB70 Debug Record.  This backfilling allows us
+// to get reproducible builds.
+void Writer::writeBuildId() {
+  // There is nothing to backfill if BuildId was not setup.
+  if (BuildId == nullptr)
+    return;
+
+  MD5 Hash;
+  MD5::MD5Result Res;
+
+  Hash.update(ArrayRef<uint8_t>{Buffer->getBufferStart(),
+                                Buffer->getBufferEnd()});
+  Hash.final(Res);
+
+  assert(BuildId->DI->Signature.CVSignature == OMF::Signature::PDB70 &&
+         "only PDB 7.0 is supported");
+  assert(sizeof(Res) == sizeof(BuildId->DI->PDB70.Signature) &&
+         "signature size mismatch");
+  memcpy(BuildId->DI->PDB70.Signature, Res,
+         sizeof(codeview::PDB70DebugInfo::Signature));
+  // TODO(compnerd) track the Age
+  BuildId->DI->PDB70.Age = 1;
+}
+
 OutputSection *Writer::findSection(StringRef Name) {
   for (OutputSection *Sec : OutputSections)
     if (Sec->getName() == Name)
@@ -744,16 +865,13 @@ OutputSection *Writer::createSection(StringRef Name) {
   uint32_t Perms = StringSwitch<uint32_t>(Name)
                        .Case(".bss", BSS | R | W)
                        .Case(".data", DATA | R | W)
-                       .Case(".didat", DATA | R)
-                       .Case(".edata", DATA | R)
-                       .Case(".idata", DATA | R)
-                       .Case(".rdata", DATA | R)
+                       .Cases(".didat", ".edata", ".idata", ".rdata", DATA | R)
                        .Case(".reloc", DATA | DISCARDABLE | R)
                        .Case(".text", CODE | R | X)
                        .Default(0);
   if (!Perms)
     llvm_unreachable("unknown section name");
-  auto Sec = new (CAlloc.Allocate()) OutputSection(Name);
+  auto Sec = make<OutputSection>(Name);
   Sec->addPermissions(Perms);
   OutputSections.push_back(Sec);
   return Sec;
@@ -784,13 +902,11 @@ void Writer::addBaserelBlocks(OutputSection *Dest, std::vector<Baserel> &V) {
     uint32_t P = V[J].RVA & Mask;
     if (P == Page)
       continue;
-    BaserelChunk *Buf = BAlloc.Allocate();
-    Dest->addChunk(new (Buf) BaserelChunk(Page, &V[I], &V[0] + J));
+    Dest->addChunk(make<BaserelChunk>(Page, &V[I], &V[0] + J));
     I = J;
     Page = P;
   }
   if (I == J)
     return;
-  BaserelChunk *Buf = BAlloc.Allocate();
-  Dest->addChunk(new (Buf) BaserelChunk(Page, &V[I], &V[0] + J));
+  Dest->addChunk(make<BaserelChunk>(Page, &V[I], &V[0] + J));
 }
diff --git a/COFF/Writer.h b/COFF/Writer.h
index 0473315ae50a..0d26090177d8 100644
--- a/COFF/Writer.h
+++ b/COFF/Writer.h
@@ -14,9 +14,7 @@
 
 namespace lld {
 namespace coff {
-
-class Chunk;
-class OutputSection;
+class SymbolTable;
 
 void writeResult(SymbolTable *T);
 
diff --git a/ELF/CMakeLists.txt b/ELF/CMakeLists.txt
index a1b65adc7400..2e9d2b941fd9 100644
--- a/ELF/CMakeLists.txt
+++ b/ELF/CMakeLists.txt
@@ -2,24 +2,30 @@ set(LLVM_TARGET_DEFINITIONS Options.td)
 tablegen(LLVM Options.inc -gen-opt-parser-defs)
 add_public_tablegen_target(ELFOptionsTableGen)
 
+if(NOT LLD_BUILT_STANDALONE)
+  set(tablegen_deps intrinsics_gen)
+endif()
+
 add_lld_library(lldELF
   Driver.cpp
   DriverUtils.cpp
   EhFrame.cpp
   Error.cpp
+  GdbIndex.cpp
   ICF.cpp
   InputFiles.cpp
   InputSection.cpp
   LTO.cpp
   LinkerScript.cpp
   MarkLive.cpp
+  Mips.cpp
   OutputSections.cpp
   Relocations.cpp
   ScriptParser.cpp
   Strings.cpp
-  SymbolListFile.cpp
   SymbolTable.cpp
   Symbols.cpp
+  SyntheticSections.cpp
   Target.cpp
   Thunks.cpp
   Writer.cpp
@@ -31,6 +37,8 @@ add_lld_library(lldELF
   BitWriter
   Codegen
   Core
+  DebugInfoDWARF
+  Demangle
   IPO
   Linker
   LTO
@@ -44,7 +52,10 @@ add_lld_library(lldELF
 
   LINK_LIBS
   lldConfig
+  lldCore
   ${PTHREAD_LIB}
-  )
 
-add_dependencies(lldELF intrinsics_gen ELFOptionsTableGen)
+  DEPENDS
+  ELFOptionsTableGen
+  ${tablegen_deps}
+  )
diff --git a/ELF/Config.h b/ELF/Config.h
index 2ccd95e88775..b828cdb25047 100644
--- a/ELF/Config.h
+++ b/ELF/Config.h
@@ -12,6 +12,7 @@
 
 #include "llvm/ADT/MapVector.h"
 #include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/StringSet.h"
 #include "llvm/Support/ELF.h"
 
 #include <vector>
@@ -30,21 +31,36 @@ enum ELFKind {
   ELF64BEKind
 };
 
-enum class BuildIdKind { None, Fnv1, Md5, Sha1, Hexstring };
+// For --build-id.
+enum class BuildIdKind { None, Fast, Md5, Sha1, Hexstring, Uuid };
 
-enum class UnresolvedPolicy { NoUndef, Error, Warn, Ignore };
+// For --discard-{all,locals,none} and --retain-symbols-file.
+enum class DiscardPolicy { Default, All, Locals, RetainFile, None };
+
+// For --strip-{all,debug}.
+enum class StripPolicy { None, All, Debug };
+
+// For --unresolved-symbols.
+enum class UnresolvedPolicy { NoUndef, ReportError, Warn, Ignore };
+
+// For --sort-section and linkerscript sorting rules.
+enum class SortSectionPolicy { Default, None, Alignment, Name, Priority };
+
+// For --target2
+enum class Target2Policy { Abs, Rel, GotRel };
 
 struct SymbolVersion {
   llvm::StringRef Name;
   bool IsExternCpp;
+  bool HasWildcard;
 };
 
 // This struct contains symbols version definition that
 // can be found in version script if it is used for link.
 struct VersionDefinition {
-  VersionDefinition(llvm::StringRef Name, size_t Id) : Name(Name), Id(Id) {}
+  VersionDefinition(llvm::StringRef Name, uint16_t Id) : Name(Name), Id(Id) {}
   llvm::StringRef Name;
-  size_t Id;
+  uint16_t Id;
   std::vector<SymbolVersion> Globals;
   size_t NameOff; // Offset in string table.
 };
@@ -54,75 +70,92 @@ struct VersionDefinition {
 // and such fields have the same name as the corresponding options.
 // Most fields are initialized by the driver.
 struct Configuration {
-  Symbol *EntrySym = nullptr;
   InputFile *FirstElf = nullptr;
+  uint8_t OSABI = 0;
+  llvm::StringMap<uint64_t> SectionStartMap;
   llvm::StringRef DynamicLinker;
   llvm::StringRef Entry;
   llvm::StringRef Emulation;
   llvm::StringRef Fini;
   llvm::StringRef Init;
-  llvm::StringRef LtoAAPipeline;
-  llvm::StringRef LtoNewPmPasses;
+  llvm::StringRef LTOAAPipeline;
+  llvm::StringRef LTONewPmPasses;
   llvm::StringRef OutputFile;
   llvm::StringRef SoName;
   llvm::StringRef Sysroot;
+  llvm::StringSet<> RetainSymbolsFile;
   std::string RPath;
   std::vector<VersionDefinition> VersionDefinitions;
-  std::vector<llvm::StringRef> DynamicList;
+  std::vector<llvm::StringRef> AuxiliaryList;
   std::vector<llvm::StringRef> SearchPaths;
+  std::vector<llvm::StringRef> SymbolOrderingFile;
   std::vector<llvm::StringRef> Undefined;
   std::vector<SymbolVersion> VersionScriptGlobals;
+  std::vector<SymbolVersion> VersionScriptLocals;
   std::vector<uint8_t> BuildIdVector;
   bool AllowMultipleDefinition;
   bool AsNeeded = false;
   bool Bsymbolic;
   bool BsymbolicFunctions;
+  bool ColorDiagnostics = false;
   bool Demangle = true;
   bool DisableVerify;
-  bool DiscardAll;
-  bool DiscardLocals;
-  bool DiscardNone;
   bool EhFrameHdr;
   bool EnableNewDtags;
   bool ExportDynamic;
   bool FatalWarnings;
   bool GcSections;
+  bool GdbIndex;
   bool GnuHash = false;
   bool ICF;
   bool Mips64EL = false;
+  bool MipsN32Abi = false;
   bool NoGnuUnique;
   bool NoUndefinedVersion;
+  bool Nostdlib;
+  bool OFormatBinary;
+  bool OMagic;
   bool Pic;
   bool Pie;
   bool PrintGcSections;
   bool Rela;
   bool Relocatable;
   bool SaveTemps;
+  bool SingleRoRx;
   bool Shared;
   bool Static = false;
-  bool StripAll;
-  bool StripDebug;
   bool SysvHash = true;
+  bool Target1Rel;
   bool Threads;
   bool Trace;
   bool Verbose;
   bool WarnCommon;
+  bool WarnMissingEntry;
   bool ZCombreloc;
-  bool ZExecStack;
+  bool ZExecstack;
   bool ZNodelete;
   bool ZNow;
   bool ZOrigin;
   bool ZRelro;
+  bool ExitEarly;
+  bool ZWxneeded;
+  DiscardPolicy Discard;
+  SortSectionPolicy SortSection;
+  StripPolicy Strip = StripPolicy::None;
   UnresolvedPolicy UnresolvedSymbols;
+  Target2Policy Target2 = Target2Policy::GotRel;
   BuildIdKind BuildId = BuildIdKind::None;
   ELFKind EKind = ELFNoneKind;
   uint16_t DefaultSymbolVersion = llvm::ELF::VER_NDX_GLOBAL;
   uint16_t EMachine = llvm::ELF::EM_NONE;
-  uint64_t EntryAddr = -1;
+  uint64_t ErrorLimit = 20;
   uint64_t ImageBase;
-  unsigned LtoJobs;
-  unsigned LtoO;
+  uint64_t MaxPageSize;
+  uint64_t ZStackSize;
+  unsigned LTOPartitions;
+  unsigned LTOO;
   unsigned Optimize;
+  unsigned ThinLTOJobs;
 };
 
 // The only instance of Configuration struct.
diff --git a/ELF/Driver.cpp b/ELF/Driver.cpp
index c6ca2639236f..a11dbc7cc47f 100644
--- a/ELF/Driver.cpp
+++ b/ELF/Driver.cpp
@@ -14,14 +14,17 @@
 #include "InputFiles.h"
 #include "InputSection.h"
 #include "LinkerScript.h"
+#include "Memory.h"
 #include "Strings.h"
-#include "SymbolListFile.h"
 #include "SymbolTable.h"
 #include "Target.h"
+#include "Threads.h"
 #include "Writer.h"
+#include "lld/Config/Version.h"
 #include "lld/Driver/Driver.h"
 #include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/StringSwitch.h"
+#include "llvm/Support/CommandLine.h"
 #include "llvm/Support/TargetSelect.h"
 #include "llvm/Support/raw_ostream.h"
 #include <cstdlib>
@@ -38,48 +41,59 @@ using namespace lld::elf;
 Configuration *elf::Config;
 LinkerDriver *elf::Driver;
 
-bool elf::link(ArrayRef<const char *> Args, raw_ostream &Error) {
-  HasError = false;
+BumpPtrAllocator elf::BAlloc;
+StringSaver elf::Saver{BAlloc};
+std::vector<SpecificAllocBase *> elf::SpecificAllocBase::Instances;
+
+bool elf::link(ArrayRef<const char *> Args, bool CanExitEarly,
+               raw_ostream &Error) {
+  ErrorCount = 0;
   ErrorOS = &Error;
+  Argv0 = Args[0];
 
-  Configuration C;
-  LinkerDriver D;
-  ScriptConfiguration SC;
-  Config = &C;
-  Driver = &D;
-  ScriptConfig = &SC;
+  Config = make<Configuration>();
+  Driver = make<LinkerDriver>();
+  ScriptConfig = make<ScriptConfiguration>();
 
-  Driver->main(Args);
-  return !HasError;
+  Driver->main(Args, CanExitEarly);
+  freeArena();
+  return !ErrorCount;
 }
 
 // Parses a linker -m option.
-static std::pair<ELFKind, uint16_t> parseEmulation(StringRef S) {
-  if (S.endswith("_fbsd"))
+static std::tuple<ELFKind, uint16_t, uint8_t> parseEmulation(StringRef Emul) {
+  uint8_t OSABI = 0;
+  StringRef S = Emul;
+  if (S.endswith("_fbsd")) {
     S = S.drop_back(5);
+    OSABI = ELFOSABI_FREEBSD;
+  }
 
   std::pair<ELFKind, uint16_t> Ret =
       StringSwitch<std::pair<ELFKind, uint16_t>>(S)
-          .Case("aarch64linux", {ELF64LEKind, EM_AARCH64})
+          .Cases("aarch64elf", "aarch64linux", {ELF64LEKind, EM_AARCH64})
           .Case("armelf_linux_eabi", {ELF32LEKind, EM_ARM})
           .Case("elf32_x86_64", {ELF32LEKind, EM_X86_64})
           .Case("elf32btsmip", {ELF32BEKind, EM_MIPS})
           .Case("elf32ltsmip", {ELF32LEKind, EM_MIPS})
+          .Case("elf32btsmipn32", {ELF32BEKind, EM_MIPS})
+          .Case("elf32ltsmipn32", {ELF32LEKind, EM_MIPS})
           .Case("elf32ppc", {ELF32BEKind, EM_PPC})
           .Case("elf64btsmip", {ELF64BEKind, EM_MIPS})
           .Case("elf64ltsmip", {ELF64LEKind, EM_MIPS})
           .Case("elf64ppc", {ELF64BEKind, EM_PPC64})
+          .Cases("elf_amd64", "elf_x86_64", {ELF64LEKind, EM_X86_64})
           .Case("elf_i386", {ELF32LEKind, EM_386})
-          .Case("elf_x86_64", {ELF64LEKind, EM_X86_64})
+          .Case("elf_iamcu", {ELF32LEKind, EM_IAMCU})
           .Default({ELFNoneKind, EM_NONE});
 
   if (Ret.first == ELFNoneKind) {
     if (S == "i386pe" || S == "i386pep" || S == "thumb2pe")
-      error("Windows targets are not supported on the ELF frontend: " + S);
+      error("Windows targets are not supported on the ELF frontend: " + Emul);
     else
-      error("unknown emulation: " + S);
+      error("unknown emulation: " + Emul);
   }
-  return Ret;
+  return std::make_tuple(Ret.first, Ret.second, OSABI);
 }
 
 // Returns slices of MB by parsing MB as an archive file.
@@ -87,25 +101,28 @@ static std::pair<ELFKind, uint16_t> parseEmulation(StringRef S) {
 std::vector<MemoryBufferRef>
 LinkerDriver::getArchiveMembers(MemoryBufferRef MB) {
   std::unique_ptr<Archive> File =
-      check(Archive::create(MB), "failed to parse archive");
+      check(Archive::create(MB),
+            MB.getBufferIdentifier() + ": failed to parse archive");
 
   std::vector<MemoryBufferRef> V;
-  Error Err;
+  Error Err = Error::success();
   for (const ErrorOr<Archive::Child> &COrErr : File->children(Err)) {
-    Archive::Child C = check(COrErr, "could not get the child of the archive " +
-                                         File->getFileName());
+    Archive::Child C =
+        check(COrErr, MB.getBufferIdentifier() +
+                          ": could not get the child of the archive");
     MemoryBufferRef MBRef =
         check(C.getMemoryBufferRef(),
-              "could not get the buffer for a child of the archive " +
-                  File->getFileName());
+              MB.getBufferIdentifier() +
+                  ": could not get the buffer for a child of the archive");
     V.push_back(MBRef);
   }
   if (Err)
-    Error(Err);
+    fatal(MB.getBufferIdentifier() + ": Archive::children failed: " +
+          toString(std::move(Err)));
 
   // Take ownership of memory buffers created for members of thin archives.
   for (std::unique_ptr<MemoryBuffer> &MB : File->takeThinBuffers())
-    OwningMBs.push_back(std::move(MB));
+    make<std::unique_ptr<MemoryBuffer>>(std::move(MB));
 
   return V;
 }
@@ -114,25 +131,28 @@ LinkerDriver::getArchiveMembers(MemoryBufferRef MB) {
 // Newly created memory buffers are owned by this driver.
 void LinkerDriver::addFile(StringRef Path) {
   using namespace sys::fs;
-  if (Config->Verbose)
-    outs() << Path << "\n";
 
   Optional<MemoryBufferRef> Buffer = readFile(Path);
   if (!Buffer.hasValue())
     return;
   MemoryBufferRef MBRef = *Buffer;
 
+  if (InBinary) {
+    Files.push_back(make<BinaryFile>(MBRef));
+    return;
+  }
+
   switch (identify_magic(MBRef.getBuffer())) {
   case file_magic::unknown:
     readLinkerScript(MBRef);
     return;
   case file_magic::archive:
-    if (WholeArchive) {
+    if (InWholeArchive) {
       for (MemoryBufferRef MB : getArchiveMembers(MBRef))
         Files.push_back(createObjectFile(MB, Path));
       return;
     }
-    Files.push_back(make_unique<ArchiveFile>(MBRef));
+    Files.push_back(make<ArchiveFile>(MBRef));
     return;
   case file_magic::elf_shared_object:
     if (Config->Relocatable) {
@@ -143,13 +163,16 @@ void LinkerDriver::addFile(StringRef Path) {
     return;
   default:
     if (InLib)
-      Files.push_back(make_unique<LazyObjectFile>(MBRef));
+      Files.push_back(make<LazyObjectFile>(MBRef));
     else
       Files.push_back(createObjectFile(MBRef));
   }
 }
 
 Optional<MemoryBufferRef> LinkerDriver::readFile(StringRef Path) {
+  if (Config->Verbose)
+    outs() << Path << "\n";
+
   auto MBOrErr = MemoryBuffer::getFile(Path);
   if (auto EC = MBOrErr.getError()) {
     error(EC, "cannot open " + Path);
@@ -157,7 +180,7 @@ Optional<MemoryBufferRef> LinkerDriver::readFile(StringRef Path) {
   }
   std::unique_ptr<MemoryBuffer> &MB = *MBOrErr;
   MemoryBufferRef MBRef = MB->getMemBufferRef();
-  OwningMBs.push_back(std::move(MB)); // take MB ownership
+  make<std::unique_ptr<MemoryBuffer>>(std::move(MB)); // take MB ownership
 
   if (Cpio)
     Cpio->append(relativeToRoot(Path), MBRef.getBuffer());
@@ -167,11 +190,10 @@ Optional<MemoryBufferRef> LinkerDriver::readFile(StringRef Path) {
 
 // Add a given library by searching it from input search paths.
 void LinkerDriver::addLibrary(StringRef Name) {
-  std::string Path = searchLibrary(Name);
-  if (Path.empty())
-    error("unable to find library -l" + Name);
+  if (Optional<std::string> Path = searchLibrary(Name))
+    addFile(*Path);
   else
-    addFile(Path);
+    error("unable to find library -l" + Name);
 }
 
 // This function is called on startup. We need this for LTO since
@@ -184,12 +206,6 @@ static void initLLVM(opt::InputArgList &Args) {
   InitializeAllAsmPrinters();
   InitializeAllAsmParsers();
 
-  // This is a flag to discard all but GlobalValue names.
-  // We want to enable it by default because it saves memory.
-  // Disable it only when a developer option (-save-temps) is given.
-  Driver->Context.setDiscardValueNames(!Config->SaveTemps);
-  Driver->Context.enableDebugTypeODRUniquing();
-
   // Parse and evaluate -mllvm options.
   std::vector<const char *> V;
   V.push_back("lld (LLVM option parsing)");
@@ -206,9 +222,6 @@ static void checkOptions(opt::InputArgList &Args) {
   if (Config->EMachine == EM_MIPS && Config->GnuHash)
     error("the .gnu.hash section is not compatible with the MIPS target.");
 
-  if (Config->EMachine == EM_AMDGPU && !Config->Entry.empty())
-    error("-e option is not valid for AMDGPU.");
-
   if (Config->Pie && Config->Shared)
     error("-shared and -pie may not be used together");
 
@@ -224,8 +237,8 @@ static void checkOptions(opt::InputArgList &Args) {
   }
 }
 
-static StringRef
-getString(opt::InputArgList &Args, unsigned Key, StringRef Default = "") {
+static StringRef getString(opt::InputArgList &Args, unsigned Key,
+                           StringRef Default = "") {
   if (auto *Arg = Args.getLastArg(Key))
     return Arg->getValue();
   return Default;
@@ -254,33 +267,64 @@ static bool hasZOption(opt::InputArgList &Args, StringRef Key) {
   return false;
 }
 
-void LinkerDriver::main(ArrayRef<const char *> ArgsArr) {
+static uint64_t getZOptionValue(opt::InputArgList &Args, StringRef Key,
+                                uint64_t Default) {
+  for (auto *Arg : Args.filtered(OPT_z)) {
+    StringRef Value = Arg->getValue();
+    size_t Pos = Value.find("=");
+    if (Pos != StringRef::npos && Key == Value.substr(0, Pos)) {
+      Value = Value.substr(Pos + 1);
+      uint64_t Result;
+      if (Value.getAsInteger(0, Result))
+        error("invalid " + Key + ": " + Value);
+      return Result;
+    }
+  }
+  return Default;
+}
+
+void LinkerDriver::main(ArrayRef<const char *> ArgsArr, bool CanExitEarly) {
   ELFOptTable Parser;
   opt::InputArgList Args = Parser.parse(ArgsArr.slice(1));
+
+  // Interpret this flag early because error() depends on them.
+  Config->ErrorLimit = getInteger(Args, OPT_error_limit, 20);
+
+  // Handle -help
   if (Args.hasArg(OPT_help)) {
     printHelp(ArgsArr[0]);
     return;
   }
-  if (Args.hasArg(OPT_version)) {
-    outs() << getVersionString();
+
+  // GNU linkers disagree here. Though both -version and -v are mentioned
+  // in help to print the version information, GNU ld just normally exits,
+  // while gold can continue linking. We are compatible with ld.bfd here.
+  if (Args.hasArg(OPT_version) || Args.hasArg(OPT_v))
+    outs() << getLLDVersion() << "\n";
+  if (Args.hasArg(OPT_version))
     return;
-  }
+
+  Config->ExitEarly = CanExitEarly && !Args.hasArg(OPT_full_shutdown);
 
   if (const char *Path = getReproduceOption(Args)) {
     // Note that --reproduce is a debug option so you can ignore it
     // if you are trying to understand the whole picture of the code.
-    Cpio.reset(CpioFile::create(Path));
-    if (Cpio) {
+    ErrorOr<CpioFile *> F = CpioFile::create(Path);
+    if (F) {
+      Cpio.reset(*F);
       Cpio->append("response.txt", createResponseFile(Args));
-      Cpio->append("version.txt", getVersionString());
-    }
+      Cpio->append("version.txt", getLLDVersion() + "\n");
+    } else
+      error(F.getError(),
+            Twine("--reproduce: failed to open ") + Path + ".cpio");
   }
 
   readConfigs(Args);
   initLLVM(Args);
   createFiles(Args);
+  inferMachineType();
   checkOptions(Args);
-  if (HasError)
+  if (ErrorCount)
     return;
 
   switch (Config->EKind) {
@@ -297,7 +341,7 @@ void LinkerDriver::main(ArrayRef<const char *> ArgsArr) {
     link<ELF64BE>(Args);
     return;
   default:
-    error("-m or at least a .o file required");
+    llvm_unreachable("unknown Config->EKind");
   }
 }
 
@@ -314,10 +358,115 @@ static UnresolvedPolicy getUnresolvedSymbolOption(opt::InputArgList &Args) {
     if (S == "ignore-all" || S == "ignore-in-object-files")
       return UnresolvedPolicy::Ignore;
     if (S == "ignore-in-shared-libs" || S == "report-all")
-      return UnresolvedPolicy::Error;
+      return UnresolvedPolicy::ReportError;
     error("unknown --unresolved-symbols value: " + S);
   }
-  return UnresolvedPolicy::Error;
+  return UnresolvedPolicy::ReportError;
+}
+
+static Target2Policy getTarget2Option(opt::InputArgList &Args) {
+  if (auto *Arg = Args.getLastArg(OPT_target2)) {
+    StringRef S = Arg->getValue();
+    if (S == "rel")
+      return Target2Policy::Rel;
+    if (S == "abs")
+      return Target2Policy::Abs;
+    if (S == "got-rel")
+      return Target2Policy::GotRel;
+    error("unknown --target2 option: " + S);
+  }
+  return Target2Policy::GotRel;
+}
+
+static bool isOutputFormatBinary(opt::InputArgList &Args) {
+  if (auto *Arg = Args.getLastArg(OPT_oformat)) {
+    StringRef S = Arg->getValue();
+    if (S == "binary")
+      return true;
+    error("unknown --oformat value: " + S);
+  }
+  return false;
+}
+
+static bool getArg(opt::InputArgList &Args, unsigned K1, unsigned K2,
+                   bool Default) {
+  if (auto *Arg = Args.getLastArg(K1, K2))
+    return Arg->getOption().getID() == K1;
+  return Default;
+}
+
+static DiscardPolicy getDiscardOption(opt::InputArgList &Args) {
+  if (Config->Relocatable)
+    return DiscardPolicy::None;
+  auto *Arg =
+      Args.getLastArg(OPT_discard_all, OPT_discard_locals, OPT_discard_none);
+  if (!Arg)
+    return DiscardPolicy::Default;
+  if (Arg->getOption().getID() == OPT_discard_all)
+    return DiscardPolicy::All;
+  if (Arg->getOption().getID() == OPT_discard_locals)
+    return DiscardPolicy::Locals;
+  return DiscardPolicy::None;
+}
+
+static StripPolicy getStripOption(opt::InputArgList &Args) {
+  if (auto *Arg = Args.getLastArg(OPT_strip_all, OPT_strip_debug)) {
+    if (Arg->getOption().getID() == OPT_strip_all)
+      return StripPolicy::All;
+    return StripPolicy::Debug;
+  }
+  return StripPolicy::None;
+}
+
+static uint64_t parseSectionAddress(StringRef S, opt::Arg *Arg) {
+  uint64_t VA = 0;
+  if (S.startswith("0x"))
+    S = S.drop_front(2);
+  if (S.getAsInteger(16, VA))
+    error("invalid argument: " + stringize(Arg));
+  return VA;
+}
+
+static StringMap<uint64_t> getSectionStartMap(opt::InputArgList &Args) {
+  StringMap<uint64_t> Ret;
+  for (auto *Arg : Args.filtered(OPT_section_start)) {
+    StringRef Name;
+    StringRef Addr;
+    std::tie(Name, Addr) = StringRef(Arg->getValue()).split('=');
+    Ret[Name] = parseSectionAddress(Addr, Arg);
+  }
+
+  if (auto *Arg = Args.getLastArg(OPT_Ttext))
+    Ret[".text"] = parseSectionAddress(Arg->getValue(), Arg);
+  if (auto *Arg = Args.getLastArg(OPT_Tdata))
+    Ret[".data"] = parseSectionAddress(Arg->getValue(), Arg);
+  if (auto *Arg = Args.getLastArg(OPT_Tbss))
+    Ret[".bss"] = parseSectionAddress(Arg->getValue(), Arg);
+  return Ret;
+}
+
+static SortSectionPolicy getSortKind(opt::InputArgList &Args) {
+  StringRef S = getString(Args, OPT_sort_section);
+  if (S == "alignment")
+    return SortSectionPolicy::Alignment;
+  if (S == "name")
+    return SortSectionPolicy::Name;
+  if (!S.empty())
+    error("unknown --sort-section rule: " + S);
+  return SortSectionPolicy::Default;
+}
+
+static std::vector<StringRef> getLines(MemoryBufferRef MB) {
+  SmallVector<StringRef, 0> Arr;
+  MB.getBuffer().split(Arr, '\n');
+
+  std::vector<StringRef> Ret;
+  for (StringRef S : Arr) {
+    S = S.trim();
+    if (!S.empty())
+      Ret.push_back(S);
+  }
+  return Ret;
 }
 
 // Initializes Config members by the command line options.
@@ -334,34 +483,37 @@ void LinkerDriver::readConfigs(opt::InputArgList &Args) {
   if (auto *Arg = Args.getLastArg(OPT_m)) {
     // Parse ELF{32,64}{LE,BE} and CPU type.
     StringRef S = Arg->getValue();
-    std::tie(Config->EKind, Config->EMachine) = parseEmulation(S);
+    std::tie(Config->EKind, Config->EMachine, Config->OSABI) =
+        parseEmulation(S);
+    Config->MipsN32Abi = (S == "elf32btsmipn32" || S == "elf32ltsmipn32");
     Config->Emulation = S;
   }
 
   Config->AllowMultipleDefinition = Args.hasArg(OPT_allow_multiple_definition);
   Config->Bsymbolic = Args.hasArg(OPT_Bsymbolic);
   Config->BsymbolicFunctions = Args.hasArg(OPT_Bsymbolic_functions);
-  Config->Demangle = !Args.hasArg(OPT_no_demangle);
+  Config->Demangle = getArg(Args, OPT_demangle, OPT_no_demangle, true);
   Config->DisableVerify = Args.hasArg(OPT_disable_verify);
-  Config->DiscardAll = Args.hasArg(OPT_discard_all);
-  Config->DiscardLocals = Args.hasArg(OPT_discard_locals);
-  Config->DiscardNone = Args.hasArg(OPT_discard_none);
   Config->EhFrameHdr = Args.hasArg(OPT_eh_frame_hdr);
   Config->EnableNewDtags = !Args.hasArg(OPT_disable_new_dtags);
   Config->ExportDynamic = Args.hasArg(OPT_export_dynamic);
   Config->FatalWarnings = Args.hasArg(OPT_fatal_warnings);
-  Config->GcSections = Args.hasArg(OPT_gc_sections);
+  Config->GcSections = getArg(Args, OPT_gc_sections, OPT_no_gc_sections, false);
+  Config->GdbIndex = Args.hasArg(OPT_gdb_index);
   Config->ICF = Args.hasArg(OPT_icf);
   Config->NoGnuUnique = Args.hasArg(OPT_no_gnu_unique);
   Config->NoUndefinedVersion = Args.hasArg(OPT_no_undefined_version);
-  Config->Pie = Args.hasArg(OPT_pie);
+  Config->Nostdlib = Args.hasArg(OPT_nostdlib);
+  Config->OMagic = Args.hasArg(OPT_omagic);
+  Config->Pie = getArg(Args, OPT_pie, OPT_nopie, false);
   Config->PrintGcSections = Args.hasArg(OPT_print_gc_sections);
   Config->Relocatable = Args.hasArg(OPT_relocatable);
+  Config->Discard = getDiscardOption(Args);
   Config->SaveTemps = Args.hasArg(OPT_save_temps);
+  Config->SingleRoRx = Args.hasArg(OPT_no_rosegment);
   Config->Shared = Args.hasArg(OPT_shared);
-  Config->StripAll = Args.hasArg(OPT_strip_all);
-  Config->StripDebug = Args.hasArg(OPT_strip_debug);
-  Config->Threads = Args.hasArg(OPT_threads);
+  Config->Target1Rel = getArg(Args, OPT_target1_rel, OPT_target1_abs, false);
+  Config->Threads = getArg(Args, OPT_threads, OPT_no_threads, true);
   Config->Trace = Args.hasArg(OPT_trace);
   Config->Verbose = Args.hasArg(OPT_verbose);
   Config->WarnCommon = Args.hasArg(OPT_warn_common);
@@ -370,33 +522,47 @@ void LinkerDriver::readConfigs(opt::InputArgList &Args) {
   Config->Entry = getString(Args, OPT_entry);
   Config->Fini = getString(Args, OPT_fini, "_fini");
   Config->Init = getString(Args, OPT_init, "_init");
-  Config->LtoAAPipeline = getString(Args, OPT_lto_aa_pipeline);
-  Config->LtoNewPmPasses = getString(Args, OPT_lto_newpm_passes);
+  Config->LTOAAPipeline = getString(Args, OPT_lto_aa_pipeline);
+  Config->LTONewPmPasses = getString(Args, OPT_lto_newpm_passes);
   Config->OutputFile = getString(Args, OPT_o);
   Config->SoName = getString(Args, OPT_soname);
   Config->Sysroot = getString(Args, OPT_sysroot);
 
   Config->Optimize = getInteger(Args, OPT_O, 1);
-  Config->LtoO = getInteger(Args, OPT_lto_O, 2);
-  if (Config->LtoO > 3)
+  Config->LTOO = getInteger(Args, OPT_lto_O, 2);
+  if (Config->LTOO > 3)
     error("invalid optimization level for LTO: " + getString(Args, OPT_lto_O));
-  Config->LtoJobs = getInteger(Args, OPT_lto_jobs, 1);
-  if (Config->LtoJobs == 0)
-    error("number of threads must be > 0");
+  Config->LTOPartitions = getInteger(Args, OPT_lto_partitions, 1);
+  if (Config->LTOPartitions == 0)
+    error("--lto-partitions: number of threads must be > 0");
+  Config->ThinLTOJobs = getInteger(Args, OPT_thinlto_jobs, -1u);
+  if (Config->ThinLTOJobs == 0)
+    error("--thinlto-jobs: number of threads must be > 0");
 
   Config->ZCombreloc = !hasZOption(Args, "nocombreloc");
-  Config->ZExecStack = hasZOption(Args, "execstack");
+  Config->ZExecstack = hasZOption(Args, "execstack");
   Config->ZNodelete = hasZOption(Args, "nodelete");
   Config->ZNow = hasZOption(Args, "now");
   Config->ZOrigin = hasZOption(Args, "origin");
   Config->ZRelro = !hasZOption(Args, "norelro");
+  Config->ZStackSize = getZOptionValue(Args, "stack-size", -1);
+  Config->ZWxneeded = hasZOption(Args, "wxneeded");
 
-  if (Config->Relocatable)
-    Config->StripAll = false;
+  Config->OFormatBinary = isOutputFormatBinary(Args);
+  Config->SectionStartMap = getSectionStartMap(Args);
+  Config->SortSection = getSortKind(Args);
+  Config->Target2 = getTarget2Option(Args);
+  Config->UnresolvedSymbols = getUnresolvedSymbolOption(Args);
+
+  // --omagic is an option to create old-fashioned executables in which
+  // .text segments are writable. Today, the option is still in use to
+  // create special-purpose programs such as boot loaders. It doesn't
+  // make sense to create PT_GNU_RELRO for such executables.
+  if (Config->OMagic)
+    Config->ZRelro = false;
 
-  // --strip-all implies --strip-debug.
-  if (Config->StripAll)
-    Config->StripDebug = true;
+  if (!Config->Relocatable)
+    Config->Strip = getStripOption(Args);
 
   // Config->Pic is true if we are generating position-independent code.
   Config->Pic = Config->Pie || Config->Shared;
@@ -414,13 +580,15 @@ void LinkerDriver::readConfigs(opt::InputArgList &Args) {
 
   // Parse --build-id or --build-id=<style>.
   if (Args.hasArg(OPT_build_id))
-    Config->BuildId = BuildIdKind::Fnv1;
+    Config->BuildId = BuildIdKind::Fast;
   if (auto *Arg = Args.getLastArg(OPT_build_id_eq)) {
     StringRef S = Arg->getValue();
     if (S == "md5") {
       Config->BuildId = BuildIdKind::Md5;
-    } else if (S == "sha1") {
+    } else if (S == "sha1" || S == "tree") {
       Config->BuildId = BuildIdKind::Sha1;
+    } else if (S == "uuid") {
+      Config->BuildId = BuildIdKind::Uuid;
     } else if (S == "none") {
       Config->BuildId = BuildIdKind::None;
     } else if (S.startswith("0x")) {
@@ -431,21 +599,58 @@ void LinkerDriver::readConfigs(opt::InputArgList &Args) {
     }
   }
 
+  for (auto *Arg : Args.filtered(OPT_auxiliary))
+    Config->AuxiliaryList.push_back(Arg->getValue());
+  if (!Config->Shared && !Config->AuxiliaryList.empty())
+    error("-f may not be used without -shared");
+
   for (auto *Arg : Args.filtered(OPT_undefined))
     Config->Undefined.push_back(Arg->getValue());
 
-  Config->UnresolvedSymbols = getUnresolvedSymbolOption(Args);
-
   if (auto *Arg = Args.getLastArg(OPT_dynamic_list))
     if (Optional<MemoryBufferRef> Buffer = readFile(Arg->getValue()))
-      parseDynamicList(*Buffer);
+      readDynamicList(*Buffer);
+
+  if (auto *Arg = Args.getLastArg(OPT_symbol_ordering_file))
+    if (Optional<MemoryBufferRef> Buffer = readFile(Arg->getValue()))
+      Config->SymbolOrderingFile = getLines(*Buffer);
+
+  // If --retain-symbol-file is used, we'll retail only the symbols listed in
+  // the file and discard all others.
+  if (auto *Arg = Args.getLastArg(OPT_retain_symbols_file)) {
+    Config->Discard = DiscardPolicy::RetainFile;
+    if (Optional<MemoryBufferRef> Buffer = readFile(Arg->getValue()))
+      for (StringRef S : getLines(*Buffer))
+        Config->RetainSymbolsFile.insert(S);
+  }
 
   for (auto *Arg : Args.filtered(OPT_export_dynamic_symbol))
-    Config->DynamicList.push_back(Arg->getValue());
+    Config->VersionScriptGlobals.push_back(
+        {Arg->getValue(), /*IsExternCpp*/ false, /*HasWildcard*/ false});
+
+  // Dynamic lists are a simplified linker script that doesn't need the
+  // "global:" and implicitly ends with a "local:*". Set the variables needed to
+  // simulate that.
+  if (Args.hasArg(OPT_dynamic_list) || Args.hasArg(OPT_export_dynamic_symbol)) {
+    Config->ExportDynamic = true;
+    if (!Config->Shared)
+      Config->DefaultSymbolVersion = VER_NDX_LOCAL;
+  }
 
   if (auto *Arg = Args.getLastArg(OPT_version_script))
     if (Optional<MemoryBufferRef> Buffer = readFile(Arg->getValue()))
-      parseVersionScript(*Buffer);
+      readVersionScript(*Buffer);
+}
+
+// Returns a value of "-format" option.
+static bool getBinaryOption(StringRef S) {
+  if (S == "binary")
+    return true;
+  if (S == "elf" || S == "default")
+    return false;
+  error("unknown -format value: " + S +
+        " (supported formats: elf, default, binary)");
+  return false;
 }
 
 void LinkerDriver::createFiles(opt::InputArgList &Args) {
@@ -454,14 +659,20 @@ void LinkerDriver::createFiles(opt::InputArgList &Args) {
     case OPT_l:
       addLibrary(Arg->getValue());
       break;
-    case OPT_alias_script_T:
     case OPT_INPUT:
-    case OPT_script:
       addFile(Arg->getValue());
       break;
+    case OPT_alias_script_T:
+    case OPT_script:
+      if (Optional<MemoryBufferRef> MB = readFile(Arg->getValue()))
+        readLinkerScript(*MB);
+      break;
     case OPT_as_needed:
       Config->AsNeeded = true;
       break;
+    case OPT_format:
+      InBinary = getBinaryOption(Arg->getValue());
+      break;
     case OPT_no_as_needed:
       Config->AsNeeded = false;
       break;
@@ -472,10 +683,10 @@ void LinkerDriver::createFiles(opt::InputArgList &Args) {
       Config->Static = false;
       break;
     case OPT_whole_archive:
-      WholeArchive = true;
+      InWholeArchive = true;
       break;
     case OPT_no_whole_archive:
-      WholeArchive = false;
+      InWholeArchive = false;
       break;
     case OPT_start_lib:
       InLib = true;
@@ -486,19 +697,55 @@ void LinkerDriver::createFiles(opt::InputArgList &Args) {
     }
   }
 
-  if (Files.empty() && !HasError)
-    error("no input files.");
+  if (Files.empty() && ErrorCount == 0)
+    error("no input files");
+}
 
-  // If -m <machine_type> was not given, infer it from object files.
-  if (Config->EKind == ELFNoneKind) {
-    for (std::unique_ptr<InputFile> &F : Files) {
-      if (F->EKind == ELFNoneKind)
-        continue;
-      Config->EKind = F->EKind;
-      Config->EMachine = F->EMachine;
-      break;
-    }
+// If -m <machine_type> was not given, infer it from object files.
+void LinkerDriver::inferMachineType() {
+  if (Config->EKind != ELFNoneKind)
+    return;
+
+  for (InputFile *F : Files) {
+    if (F->EKind == ELFNoneKind)
+      continue;
+    Config->EKind = F->EKind;
+    Config->EMachine = F->EMachine;
+    Config->OSABI = F->OSABI;
+    Config->MipsN32Abi = Config->EMachine == EM_MIPS && isMipsN32Abi(F);
+    return;
   }
+  error("target emulation unknown: -m or at least one .o file required");
+}
+
+// Parse -z max-page-size=<value>. The default value is defined by
+// each target.
+static uint64_t getMaxPageSize(opt::InputArgList &Args) {
+  uint64_t Val =
+      getZOptionValue(Args, "max-page-size", Target->DefaultMaxPageSize);
+  if (!isPowerOf2_64(Val))
+    error("max-page-size: value isn't a power of 2");
+  return Val;
+}
+
+// Parses -image-base option.
+static uint64_t getImageBase(opt::InputArgList &Args) {
+  // Use default if no -image-base option is given.
+  // Because we are using "Target" here, this function
+  // has to be called after the variable is initialized.
+  auto *Arg = Args.getLastArg(OPT_image_base);
+  if (!Arg)
+    return Config->Pic ? 0 : Target->DefaultImageBase;
+
+  StringRef S = Arg->getValue();
+  uint64_t V;
+  if (S.getAsInteger(0, V)) {
+    error("-image-base: number expected, but got " + S);
+    return 0;
+  }
+  if ((V % Config->MaxPageSize) != 0)
+    warn("-image-base: address isn't multiple of page size: " + S);
+  return V;
 }
 
 // Do actual linking. Note that when this function is called,
@@ -506,66 +753,70 @@ void LinkerDriver::createFiles(opt::InputArgList &Args) {
 template <class ELFT> void LinkerDriver::link(opt::InputArgList &Args) {
   SymbolTable<ELFT> Symtab;
   elf::Symtab<ELFT>::X = &Symtab;
+  Target = createTarget();
+  ScriptBase = Script<ELFT>::X = make<LinkerScript<ELFT>>();
 
-  std::unique_ptr<TargetInfo> TI(createTarget());
-  Target = TI.get();
-  LinkerScript<ELFT> LS;
-  Script<ELFT>::X = &LS;
-
-  Config->Rela = ELFT::Is64Bits || Config->EMachine == EM_X86_64;
+  Config->Rela =
+      ELFT::Is64Bits || Config->EMachine == EM_X86_64 || Config->MipsN32Abi;
   Config->Mips64EL =
       (Config->EMachine == EM_MIPS && Config->EKind == ELF64LEKind);
-
-  // Add entry symbol. Note that AMDGPU binaries have no entry points.
-  if (Config->Entry.empty() && !Config->Shared && !Config->Relocatable &&
-      Config->EMachine != EM_AMDGPU)
-    Config->Entry = (Config->EMachine == EM_MIPS) ? "__start" : "_start";
+  Config->MaxPageSize = getMaxPageSize(Args);
+  Config->ImageBase = getImageBase(Args);
 
   // Default output filename is "a.out" by the Unix tradition.
   if (Config->OutputFile.empty())
     Config->OutputFile = "a.out";
 
+  // Use default entry point name if no name was given via the command
+  // line nor linker scripts. For some reason, MIPS entry point name is
+  // different from others.
+  Config->WarnMissingEntry =
+      (!Config->Entry.empty() || (!Config->Shared && !Config->Relocatable));
+  if (Config->Entry.empty() && !Config->Relocatable)
+    Config->Entry = (Config->EMachine == EM_MIPS) ? "__start" : "_start";
+
   // Handle --trace-symbol.
   for (auto *Arg : Args.filtered(OPT_trace_symbol))
     Symtab.trace(Arg->getValue());
 
-  // Set either EntryAddr (if S is a number) or EntrySym (otherwise).
-  if (!Config->Entry.empty()) {
-    StringRef S = Config->Entry;
-    if (S.getAsInteger(0, Config->EntryAddr))
-      Config->EntrySym = Symtab.addUndefined(S);
-  }
+  // Add all files to the symbol table. This will add almost all
+  // symbols that we need to the symbol table.
+  for (InputFile *F : Files)
+    Symtab.addFile(F);
 
-  // Initialize Config->ImageBase.
-  if (auto *Arg = Args.getLastArg(OPT_image_base)) {
-    StringRef S = Arg->getValue();
-    if (S.getAsInteger(0, Config->ImageBase))
-      error(Arg->getSpelling() + ": number expected, but got " + S);
-    else if ((Config->ImageBase % Target->PageSize) != 0)
-      warning(Arg->getSpelling() + ": address isn't multiple of page size");
-  } else {
-    Config->ImageBase = Config->Pic ? 0 : Target->DefaultImageBase;
-  }
+  // If an entry symbol is in a static archive, pull out that file now
+  // to complete the symbol table. After this, no new names except a
+  // few linker-synthesized ones will be added to the symbol table.
+  if (Symtab.find(Config->Entry))
+    Symtab.addUndefined(Config->Entry);
 
-  for (std::unique_ptr<InputFile> &F : Files)
-    Symtab.addFile(std::move(F));
-  if (HasError)
-    return; // There were duplicate symbols or incompatible files
+  // Return if there were name resolution errors.
+  if (ErrorCount)
+    return;
 
   Symtab.scanUndefinedFlags();
   Symtab.scanShlibUndefined();
-  Symtab.scanDynamicList();
   Symtab.scanVersionScript();
-  Symtab.scanSymbolVersions();
 
-  Symtab.addCombinedLtoObject();
-  if (HasError)
+  Symtab.addCombinedLTOObject();
+  if (ErrorCount)
     return;
 
   for (auto *Arg : Args.filtered(OPT_wrap))
     Symtab.wrap(Arg->getValue());
 
-  // Write the result to the file.
+  // Now that we have a complete list of input files.
+  // Beyond this point, no new files are added.
+  // Aggregate all input sections into one place.
+  for (elf::ObjectFile<ELFT> *F : Symtab.getObjectFiles())
+    for (InputSectionBase<ELFT> *S : F->getSections())
+      if (S && S != &InputSection<ELFT>::Discarded)
+        Symtab.Sections.push_back(S);
+  for (BinaryFile *F : Symtab.getBinaryFiles())
+    for (InputSectionData *S : F->getSections())
+      Symtab.Sections.push_back(cast<InputSection<ELFT>>(S));
+
+  // Do size optimizations: garbage collection and identical code folding.
   if (Config->GcSections)
     markLive<ELFT>();
   if (Config->ICF)
@@ -573,16 +824,16 @@ template <class ELFT> void LinkerDriver::link(opt::InputArgList &Args) {
 
   // MergeInputSection::splitIntoPieces needs to be called before
   // any call of MergeInputSection::getOffset. Do that.
-  for (const std::unique_ptr<elf::ObjectFile<ELFT>> &F :
-       Symtab.getObjectFiles())
-    for (InputSectionBase<ELFT> *S : F->getSections()) {
-      if (!S || S == &InputSection<ELFT>::Discarded || !S->Live)
-        continue;
-      if (S->Compressed)
-        S->uncompress();
-      if (auto *MS = dyn_cast<MergeInputSection<ELFT>>(S))
-        MS->splitIntoPieces();
-    }
+  forEach(Symtab.Sections.begin(), Symtab.Sections.end(),
+          [](InputSectionBase<ELFT> *S) {
+            if (!S->Live)
+              return;
+            if (S->isCompressed())
+              S->uncompress();
+            if (auto *MS = dyn_cast<MergeInputSection<ELFT>>(S))
+              MS->splitIntoPieces();
+          });
 
-  writeResult<ELFT>(&Symtab);
+  // Write the result to the file.
+  writeResult<ELFT>();
 }
diff --git a/ELF/Driver.h b/ELF/Driver.h
index 6b9b9bb208e5..cba1eb164fdd 100644
--- a/ELF/Driver.h
+++ b/ELF/Driver.h
@@ -12,6 +12,7 @@
 
 #include "SymbolTable.h"
 #include "lld/Core/LLVM.h"
+#include "lld/Core/Reproduce.h"
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/StringSet.h"
@@ -23,14 +24,11 @@ namespace elf {
 
 extern class LinkerDriver *Driver;
 
-class CpioFile;
-
 class LinkerDriver {
 public:
-  void main(ArrayRef<const char *> Args);
+  void main(ArrayRef<const char *> Args, bool CanExitEarly);
   void addFile(StringRef Path);
   void addLibrary(StringRef Name);
-  llvm::LLVMContext Context;      // to parse bitcode ifles
   std::unique_ptr<CpioFile> Cpio; // for reproduce
 
 private:
@@ -38,17 +36,19 @@ private:
   llvm::Optional<MemoryBufferRef> readFile(StringRef Path);
   void readConfigs(llvm::opt::InputArgList &Args);
   void createFiles(llvm::opt::InputArgList &Args);
+  void inferMachineType();
   template <class ELFT> void link(llvm::opt::InputArgList &Args);
 
   // True if we are in --whole-archive and --no-whole-archive.
-  bool WholeArchive = false;
+  bool InWholeArchive = false;
 
   // True if we are in --start-lib and --end-lib.
   bool InLib = false;
 
-  llvm::BumpPtrAllocator Alloc;
-  std::vector<std::unique_ptr<InputFile>> Files;
-  std::vector<std::unique_ptr<MemoryBuffer>> OwningMBs;
+  // True if we are in -format=binary and -format=elf.
+  bool InBinary = false;
+
+  std::vector<InputFile *> Files;
 };
 
 // Parses command line options.
@@ -56,9 +56,6 @@ class ELFOptTable : public llvm::opt::OptTable {
 public:
   ELFOptTable();
   llvm::opt::InputArgList parse(ArrayRef<const char *> Argv);
-
-private:
-  llvm::BumpPtrAllocator Alloc;
 };
 
 // Create enum with OPT_xxx values for each option in Options.td
@@ -69,41 +66,13 @@ enum {
 #undef OPTION
 };
 
-// This is the class to create a .cpio file for --reproduce.
-//
-// If "--reproduce foo" is given, we create a file "foo.cpio" and
-// copy all input files to the archive, along with a response file
-// to re-run the same command with the same inputs.
-// It is useful for reporting issues to LLD developers.
-//
-// Cpio as a file format is a deliberate choice. It's standardized in
-// POSIX and very easy to create. cpio command is available virtually
-// on all Unix systems. See
-// http://pubs.opengroup.org/onlinepubs/9699919799/utilities/pax.html#tag_20_92_13_07
-// for the format details.
-class CpioFile {
-public:
-  static CpioFile *create(StringRef OutputPath);
-  void append(StringRef Path, StringRef Data);
-
-private:
-  CpioFile(std::unique_ptr<llvm::raw_fd_ostream> OS, StringRef Basename);
-
-  std::unique_ptr<llvm::raw_fd_ostream> OS;
-  llvm::StringSet<> Seen;
-  std::string Basename;
-};
-
 void printHelp(const char *Argv0);
-std::string getVersionString();
 std::vector<uint8_t> parseHexstring(StringRef S);
 
 std::string createResponseFile(const llvm::opt::InputArgList &Args);
-std::string relativeToRoot(StringRef Path);
 
-std::string findFromSearchPaths(StringRef Path);
-std::string searchLibrary(StringRef Path);
-std::string buildSysrootedPath(llvm::StringRef Dir, llvm::StringRef File);
+llvm::Optional<std::string> findFromSearchPaths(StringRef Path);
+llvm::Optional<std::string> searchLibrary(StringRef Path);
 
 } // namespace elf
 } // namespace lld
diff --git a/ELF/DriverUtils.cpp b/ELF/DriverUtils.cpp
index 3f18259b4ae7..a81b133f674b 100644
--- a/ELF/DriverUtils.cpp
+++ b/ELF/DriverUtils.cpp
@@ -15,14 +15,18 @@
 
 #include "Driver.h"
 #include "Error.h"
+#include "Memory.h"
+#include "ScriptParser.h"
 #include "lld/Config/Version.h"
+#include "lld/Core/Reproduce.h"
+#include "llvm/ADT/Optional.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/Triple.h"
 #include "llvm/Option/Option.h"
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Path.h"
-#include "llvm/Support/StringSaver.h"
+#include "llvm/Support/Process.h"
 
 using namespace llvm;
 using namespace llvm::sys;
@@ -40,16 +44,37 @@ using namespace lld::elf;
 // Create table mapping all options defined in Options.td
 static const opt::OptTable::Info OptInfo[] = {
 #define OPTION(X1, X2, ID, KIND, GROUP, ALIAS, X6, X7, X8, X9, X10)            \
-  {                                                                            \
-    X1, X2, X9, X10, OPT_##ID, opt::Option::KIND##Class, X8, X7, OPT_##GROUP,  \
-        OPT_##ALIAS, X6                                                        \
-  },
+  {X1, X2, X9,          X10,         OPT_##ID, opt::Option::KIND##Class,       \
+   X8, X7, OPT_##GROUP, OPT_##ALIAS, X6},
 #include "Options.inc"
 #undef OPTION
 };
 
 ELFOptTable::ELFOptTable() : OptTable(OptInfo) {}
 
+// Parse -color-diagnostics={auto,always,never} or -no-color-diagnostics.
+static bool getColorDiagnostics(opt::InputArgList &Args) {
+  bool Default = (ErrorOS == &errs() && Process::StandardErrHasColors());
+
+  auto *Arg = Args.getLastArg(OPT_color_diagnostics, OPT_color_diagnostics_eq,
+                              OPT_no_color_diagnostics);
+  if (!Arg)
+    return Default;
+  if (Arg->getOption().getID() == OPT_color_diagnostics)
+    return true;
+  if (Arg->getOption().getID() == OPT_no_color_diagnostics)
+    return false;
+
+  StringRef S = Arg->getValue();
+  if (S == "auto")
+    return Default;
+  if (S == "always")
+    return true;
+  if (S != "never")
+    error("unknown option: -color-diagnostics=" + S);
+  return false;
+}
+
 static cl::TokenizerCallback getQuotingStyle(opt::InputArgList &Args) {
   if (auto *Arg = Args.getLastArg(OPT_rsp_quoting)) {
     StringRef S = Arg->getValue();
@@ -76,16 +101,16 @@ opt::InputArgList ELFOptTable::parse(ArrayRef<const char *> Argv) {
   // --rsp-quoting.
   opt::InputArgList Args = this->ParseArgs(Vec, MissingIndex, MissingCount);
 
-  // Expand response files. '@<filename>' is replaced by the file's contents.
-  StringSaver Saver(Alloc);
+  // Expand response files (arguments in the form of @<filename>)
+  // and then parse the argument again.
   cl::ExpandResponseFiles(Saver, getQuotingStyle(Args), Vec);
-
-  // Parse options and then do error checking.
   Args = this->ParseArgs(Vec, MissingIndex, MissingCount);
+
+  // Interpret -color-diagnostics early so that error messages
+  // for unknown flags are colored.
+  Config->ColorDiagnostics = getColorDiagnostics(Args);
   if (MissingCount)
-    error(Twine("missing arg value for \"") + Args.getArgString(MissingIndex) +
-          "\", expected " + Twine(MissingCount) +
-          (MissingCount == 1 ? " argument.\n" : " arguments"));
+    error(Twine(Args.getArgString(MissingIndex)) + ": missing argument");
 
   for (auto *Arg : Args.filtered(OPT_UNKNOWN))
     error("unknown argument: " + Arg->getSpelling());
@@ -97,115 +122,6 @@ void elf::printHelp(const char *Argv0) {
   Table.PrintHelp(outs(), Argv0, "lld", false);
 }
 
-std::string elf::getVersionString() {
-  std::string Version = getLLDVersion();
-  std::string Repo = getLLDRepositoryVersion();
-  if (Repo.empty())
-    return "LLD " + Version + "\n";
-  return "LLD " + Version + " " + Repo + "\n";
-}
-
-// Makes a given pathname an absolute path first, and then remove
-// beginning /. For example, "../foo.o" is converted to "home/john/foo.o",
-// assuming that the current directory is "/home/john/bar".
-std::string elf::relativeToRoot(StringRef Path) {
-  SmallString<128> Abs = Path;
-  if (std::error_code EC = fs::make_absolute(Abs))
-    fatal("make_absolute failed: " + EC.message());
-  path::remove_dots(Abs, /*remove_dot_dot=*/true);
-
-  // This is Windows specific. root_name() returns a drive letter
-  // (e.g. "c:") or a UNC name (//net). We want to keep it as part
-  // of the result.
-  SmallString<128> Res;
-  StringRef Root = path::root_name(Abs);
-  if (Root.endswith(":"))
-    Res = Root.drop_back();
-  else if (Root.startswith("//"))
-    Res = Root.substr(2);
-
-  path::append(Res, path::relative_path(Abs));
-  return Res.str();
-}
-
-CpioFile::CpioFile(std::unique_ptr<raw_fd_ostream> OS, StringRef S)
-    : OS(std::move(OS)), Basename(S) {}
-
-CpioFile *CpioFile::create(StringRef OutputPath) {
-  std::string Path = (OutputPath + ".cpio").str();
-  std::error_code EC;
-  auto OS = llvm::make_unique<raw_fd_ostream>(Path, EC, fs::F_None);
-  if (EC) {
-    error(EC, "--reproduce: failed to open " + Path);
-    return nullptr;
-  }
-  return new CpioFile(std::move(OS), path::filename(OutputPath));
-}
-
-static void writeMember(raw_fd_ostream &OS, StringRef Path, StringRef Data) {
-  // The c_dev/c_ino pair should be unique according to the spec,
-  // but no one seems to care.
-  OS << "070707";                        // c_magic
-  OS << "000000";                        // c_dev
-  OS << "000000";                        // c_ino
-  OS << "100664";                        // c_mode: C_ISREG | rw-rw-r--
-  OS << "000000";                        // c_uid
-  OS << "000000";                        // c_gid
-  OS << "000001";                        // c_nlink
-  OS << "000000";                        // c_rdev
-  OS << "00000000000";                   // c_mtime
-  OS << format("%06o", Path.size() + 1); // c_namesize
-  OS << format("%011o", Data.size());    // c_filesize
-  OS << Path << '\0';                    // c_name
-  OS << Data;                            // c_filedata
-}
-
-void CpioFile::append(StringRef Path, StringRef Data) {
-  if (!Seen.insert(Path).second)
-    return;
-
-  // Construct an in-archive filename so that /home/foo/bar is stored
-  // as baz/home/foo/bar where baz is the basename of the output file.
-  // (i.e. in that case we are creating baz.cpio.)
-  SmallString<128> Fullpath;
-  path::append(Fullpath, Basename, Path);
-
-  // Use unix path separators so the cpio can be extracted on both unix and
-  // windows.
-  std::replace(Fullpath.begin(), Fullpath.end(), '\\', '/');
-
-  writeMember(*OS, Fullpath, Data);
-
-  // Print the trailer and seek back.
-  // This way we have a valid archive if we crash.
-  uint64_t Pos = OS->tell();
-  writeMember(*OS, "TRAILER!!!", "");
-  OS->seek(Pos);
-}
-
-// Quote a given string if it contains a space character.
-static std::string quote(StringRef S) {
-  if (S.find(' ') == StringRef::npos)
-    return S;
-  return ("\"" + S + "\"").str();
-}
-
-static std::string rewritePath(StringRef S) {
-  if (fs::exists(S))
-    return relativeToRoot(S);
-  return S;
-}
-
-static std::string stringize(opt::Arg *Arg) {
-  std::string K = Arg->getSpelling();
-  if (Arg->getNumValues() == 0)
-    return K;
-  std::string V = quote(Arg->getValue());
-  if (Arg->getOption().getRenderStyle() == opt::Option::RenderJoinedStyle)
-    return K + V;
-  return K + " " + V;
-}
-
 // Reconstructs command line arguments so that so that you can re-run
 // the same command with the same inputs. This is for --reproduce.
 std::string elf::createResponseFile(const opt::InputArgList &Args) {
@@ -226,8 +142,8 @@ std::string elf::createResponseFile(const opt::InputArgList &Args) {
     case OPT_alias_script_T:
     case OPT_script:
     case OPT_version_script:
-      OS << Arg->getSpelling() << " "
-         << quote(rewritePath(Arg->getValue())) << "\n";
+      OS << Arg->getSpelling() << " " << quote(rewritePath(Arg->getValue()))
+         << "\n";
       break;
     default:
       OS << stringize(Arg) << "\n";
@@ -236,41 +152,39 @@ std::string elf::createResponseFile(const opt::InputArgList &Args) {
   return Data.str();
 }
 
-std::string elf::findFromSearchPaths(StringRef Path) {
-  for (StringRef Dir : Config->SearchPaths) {
-    std::string FullPath = buildSysrootedPath(Dir, Path);
-    if (fs::exists(FullPath))
-      return FullPath;
-  }
-  return "";
+// Find a file by concatenating given paths. If a resulting path
+// starts with "=", the character is replaced with a --sysroot value.
+static Optional<std::string> findFile(StringRef Path1, const Twine &Path2) {
+  SmallString<128> S;
+  if (Path1.startswith("="))
+    path::append(S, Config->Sysroot, Path1.substr(1), Path2);
+  else
+    path::append(S, Path1, Path2);
+
+  if (fs::exists(S))
+    return S.str().str();
+  return None;
+}
+
+Optional<std::string> elf::findFromSearchPaths(StringRef Path) {
+  for (StringRef Dir : Config->SearchPaths)
+    if (Optional<std::string> S = findFile(Dir, Path))
+      return S;
+  return None;
 }
 
-// Searches a given library from input search paths, which are filled
-// from -L command line switches. Returns a path to an existent library file.
-std::string elf::searchLibrary(StringRef Path) {
-  if (Path.startswith(":"))
-    return findFromSearchPaths(Path.substr(1));
+// This is for -lfoo. We'll look for libfoo.so or libfoo.a from
+// search paths.
+Optional<std::string> elf::searchLibrary(StringRef Name) {
+  if (Name.startswith(":"))
+    return findFromSearchPaths(Name.substr(1));
+
   for (StringRef Dir : Config->SearchPaths) {
-    if (!Config->Static) {
-      std::string S = buildSysrootedPath(Dir, ("lib" + Path + ".so").str());
-      if (fs::exists(S))
+    if (!Config->Static)
+      if (Optional<std::string> S = findFile(Dir, "lib" + Name + ".so"))
         return S;
-    }
-    std::string S = buildSysrootedPath(Dir, ("lib" + Path + ".a").str());
-    if (fs::exists(S))
+    if (Optional<std::string> S = findFile(Dir, "lib" + Name + ".a"))
       return S;
   }
-  return "";
-}
-
-// Makes a path by concatenating Dir and File.
-// If Dir starts with '=' the result will be preceded by Sysroot,
-// which can be set with --sysroot command line switch.
-std::string elf::buildSysrootedPath(StringRef Dir, StringRef File) {
-  SmallString<128> Path;
-  if (Dir.startswith("="))
-    path::append(Path, Config->Sysroot, Dir.substr(1), File);
-  else
-    path::append(Path, Dir, File);
-  return Path.str();
+  return None;
 }
diff --git a/ELF/EhFrame.cpp b/ELF/EhFrame.cpp
index b130ac1ca22d..2428473d9012 100644
--- a/ELF/EhFrame.cpp
+++ b/ELF/EhFrame.cpp
@@ -18,6 +18,9 @@
 
 #include "EhFrame.h"
 #include "Error.h"
+#include "InputSection.h"
+#include "Relocations.h"
+#include "Strings.h"
 
 #include "llvm/Object/ELF.h"
 #include "llvm/Support/Dwarf.h"
@@ -29,49 +32,93 @@ using namespace llvm::dwarf;
 using namespace llvm::object;
 using namespace llvm::support::endian;
 
-namespace lld {
-namespace elf {
+using namespace lld;
+using namespace lld::elf;
 
+namespace {
+template <class ELFT> class EhReader {
+public:
+  EhReader(InputSectionBase<ELFT> *S, ArrayRef<uint8_t> D) : IS(S), D(D) {}
+  size_t readEhRecordSize();
+  uint8_t getFdeEncoding();
+
+private:
+  template <class P> void failOn(const P *Loc, const Twine &Msg) {
+    fatal(IS->getLocation((const uint8_t *)Loc - IS->Data.data()) + ": " + Msg);
+  }
+
+  uint8_t readByte();
+  void skipBytes(size_t Count);
+  StringRef readString();
+  void skipLeb128();
+  void skipAugP();
+
+  InputSectionBase<ELFT> *IS;
+  ArrayRef<uint8_t> D;
+};
+}
+
+template <class ELFT>
+size_t elf::readEhRecordSize(InputSectionBase<ELFT> *S, size_t Off) {
+  return EhReader<ELFT>(S, S->Data.slice(Off)).readEhRecordSize();
+}
 // .eh_frame section is a sequence of records. Each record starts with
 // a 4 byte length field. This function reads the length.
-template <class ELFT> size_t readEhRecordSize(ArrayRef<uint8_t> D) {
+template <class ELFT> size_t EhReader<ELFT>::readEhRecordSize() {
   const endianness E = ELFT::TargetEndianness;
   if (D.size() < 4)
-    fatal("CIE/FDE too small");
+    failOn(D.data(), "CIE/FDE too small");
 
   // First 4 bytes of CIE/FDE is the size of the record.
   // If it is 0xFFFFFFFF, the next 8 bytes contain the size instead,
   // but we do not support that format yet.
   uint64_t V = read32<E>(D.data());
   if (V == UINT32_MAX)
-    fatal("CIE/FDE too large");
+    failOn(D.data(), "CIE/FDE too large");
   uint64_t Size = V + 4;
   if (Size > D.size())
-    fatal("CIE/FIE ends past the end of the section");
+    failOn(D.data(), "CIE/FDE ends past the end of the section");
   return Size;
 }
 
 // Read a byte and advance D by one byte.
-static uint8_t readByte(ArrayRef<uint8_t> &D) {
+template <class ELFT> uint8_t EhReader<ELFT>::readByte() {
   if (D.empty())
-    fatal("corrupted or unsupported CIE information");
+    failOn(D.data(), "unexpected end of CIE");
   uint8_t B = D.front();
   D = D.slice(1);
   return B;
 }
 
+template <class ELFT> void EhReader<ELFT>::skipBytes(size_t Count) {
+  if (D.size() < Count)
+    failOn(D.data(), "CIE is too small");
+  D = D.slice(Count);
+}
+
+// Read a null-terminated string.
+template <class ELFT> StringRef EhReader<ELFT>::readString() {
+  const uint8_t *End = std::find(D.begin(), D.end(), '\0');
+  if (End == D.end())
+    failOn(D.data(), "corrupted CIE (failed to read string)");
+  StringRef S = toStringRef(D.slice(0, End - D.begin()));
+  D = D.slice(S.size() + 1);
+  return S;
+}
+
 // Skip an integer encoded in the LEB128 format.
 // Actual number is not of interest because only the runtime needs it.
 // But we need to be at least able to skip it so that we can read
 // the field that follows a LEB128 number.
-static void skipLeb128(ArrayRef<uint8_t> &D) {
+template <class ELFT> void EhReader<ELFT>::skipLeb128() {
+  const uint8_t *ErrPos = D.data();
   while (!D.empty()) {
     uint8_t Val = D.front();
     D = D.slice(1);
     if ((Val & 0x80) == 0)
       return;
   }
-  fatal("corrupted or unsupported CIE information");
+  failOn(ErrPos, "corrupted CIE (failed to read LEB128)");
 }
 
 template <class ELFT> static size_t getAugPSize(unsigned Enc) {
@@ -89,79 +136,79 @@ template <class ELFT> static size_t getAugPSize(unsigned Enc) {
   case DW_EH_PE_sdata8:
     return 8;
   }
-  fatal("unknown FDE encoding");
+  return 0;
 }
 
-template <class ELFT> static void skipAugP(ArrayRef<uint8_t> &D) {
-  uint8_t Enc = readByte(D);
+template <class ELFT> void EhReader<ELFT>::skipAugP() {
+  uint8_t Enc = readByte();
   if ((Enc & 0xf0) == DW_EH_PE_aligned)
-    fatal("DW_EH_PE_aligned encoding is not supported");
+    failOn(D.data() - 1, "DW_EH_PE_aligned encoding is not supported");
   size_t Size = getAugPSize<ELFT>(Enc);
+  if (Size == 0)
+    failOn(D.data() - 1, "unknown FDE encoding");
   if (Size >= D.size())
-    fatal("corrupted CIE");
+    failOn(D.data() - 1, "corrupted CIE");
   D = D.slice(Size);
 }
 
-template <class ELFT> uint8_t getFdeEncoding(ArrayRef<uint8_t> D) {
-  if (D.size() < 8)
-    fatal("CIE too small");
-  D = D.slice(8);
+template <class ELFT> uint8_t elf::getFdeEncoding(EhSectionPiece *P) {
+  auto *IS = static_cast<InputSectionBase<ELFT> *>(P->ID);
+  return EhReader<ELFT>(IS, P->data()).getFdeEncoding();
+}
 
-  uint8_t Version = readByte(D);
+template <class ELFT> uint8_t EhReader<ELFT>::getFdeEncoding() {
+  skipBytes(8);
+  int Version = readByte();
   if (Version != 1 && Version != 3)
-    fatal("FDE version 1 or 3 expected, but got " + Twine((unsigned)Version));
+    failOn(D.data() - 1,
+           "FDE version 1 or 3 expected, but got " + Twine(Version));
 
-  const unsigned char *AugEnd = std::find(D.begin(), D.end(), '\0');
-  if (AugEnd == D.end())
-    fatal("corrupted CIE");
-  StringRef Aug(reinterpret_cast<const char *>(D.begin()), AugEnd - D.begin());
-  D = D.slice(Aug.size() + 1);
+  StringRef Aug = readString();
 
-  // Code alignment factor should always be 1 for .eh_frame.
-  if (readByte(D) != 1)
-    fatal("CIE code alignment must be 1");
-
-  // Skip data alignment factor.
-  skipLeb128(D);
+  // Skip code and data alignment factors.
+  skipLeb128();
+  skipLeb128();
 
   // Skip the return address register. In CIE version 1 this is a single
   // byte. In CIE version 3 this is an unsigned LEB128.
   if (Version == 1)
-    readByte(D);
+    readByte();
   else
-    skipLeb128(D);
+    skipLeb128();
 
   // We only care about an 'R' value, but other records may precede an 'R'
   // record. Unfortunately records are not in TLV (type-length-value) format,
   // so we need to teach the linker how to skip records for each type.
   for (char C : Aug) {
     if (C == 'R')
-      return readByte(D);
+      return readByte();
     if (C == 'z') {
-      skipLeb128(D);
+      skipLeb128();
       continue;
     }
     if (C == 'P') {
-      skipAugP<ELFT>(D);
+      skipAugP();
       continue;
     }
     if (C == 'L') {
-      readByte(D);
+      readByte();
       continue;
     }
-    fatal("unknown .eh_frame augmentation string: " + Aug);
+    failOn(Aug.data(), "unknown .eh_frame augmentation string: " + Aug);
   }
   return DW_EH_PE_absptr;
 }
 
-template size_t readEhRecordSize<ELF32LE>(ArrayRef<uint8_t>);
-template size_t readEhRecordSize<ELF32BE>(ArrayRef<uint8_t>);
-template size_t readEhRecordSize<ELF64LE>(ArrayRef<uint8_t>);
-template size_t readEhRecordSize<ELF64BE>(ArrayRef<uint8_t>);
-
-template uint8_t getFdeEncoding<ELF32LE>(ArrayRef<uint8_t>);
-template uint8_t getFdeEncoding<ELF32BE>(ArrayRef<uint8_t>);
-template uint8_t getFdeEncoding<ELF64LE>(ArrayRef<uint8_t>);
-template uint8_t getFdeEncoding<ELF64BE>(ArrayRef<uint8_t>);
-}
-}
+template size_t elf::readEhRecordSize<ELF32LE>(InputSectionBase<ELF32LE> *S,
+                                               size_t Off);
+template size_t elf::readEhRecordSize<ELF32BE>(InputSectionBase<ELF32BE> *S,
+                                               size_t Off);
+template size_t elf::readEhRecordSize<ELF64LE>(InputSectionBase<ELF64LE> *S,
+                                               size_t Off);
+template size_t elf::readEhRecordSize<ELF64BE>(InputSectionBase<ELF64BE> *S,
+                                               size_t Off);
+
+template uint8_t elf::getFdeEncoding<ELF32LE>(EhSectionPiece *P);
+template uint8_t elf::getFdeEncoding<ELF32BE>(EhSectionPiece *P);
+template uint8_t elf::getFdeEncoding<ELF64LE>(EhSectionPiece *P);
+template uint8_t elf::getFdeEncoding<ELF64BE>(EhSectionPiece *P);
diff --git a/ELF/EhFrame.h b/ELF/EhFrame.h
index 0d5a2ff2f417..cadc93d3a2e4 100644
--- a/ELF/EhFrame.h
+++ b/ELF/EhFrame.h
@@ -14,8 +14,12 @@
 
 namespace lld {
 namespace elf {
-template <class ELFT> size_t readEhRecordSize(ArrayRef<uint8_t> Data);
-template <class ELFT> uint8_t getFdeEncoding(ArrayRef<uint8_t> Data);
+template <class ELFT> class InputSectionBase;
+struct EhSectionPiece;
+
+template <class ELFT>
+size_t readEhRecordSize(InputSectionBase<ELFT> *S, size_t Off);
+template <class ELFT> uint8_t getFdeEncoding(EhSectionPiece *P);
 }
 }
 
diff --git a/ELF/Error.cpp b/ELF/Error.cpp
index 59a49c17b97c..6e30f08143ed 100644
--- a/ELF/Error.cpp
+++ b/ELF/Error.cpp
@@ -12,54 +12,95 @@
 
 #include "llvm/ADT/Twine.h"
 #include "llvm/Support/Error.h"
+#include "llvm/Support/ManagedStatic.h"
 #include "llvm/Support/raw_ostream.h"
+#include <mutex>
 
+#if !defined(_MSC_VER) && !defined(__MINGW32__)
+#include <unistd.h>
+#endif
+
+using namespace lld::elf;
 using namespace llvm;
 
 namespace lld {
-namespace elf {
 
-bool HasError;
-raw_ostream *ErrorOS;
+uint64_t elf::ErrorCount;
+raw_ostream *elf::ErrorOS;
+StringRef elf::Argv0;
+
+// The functions defined in this file can be called from multiple threads,
+// but outs() or errs() are not thread-safe. We protect them using a mutex.
+static std::mutex Mu;
+
+static void print(StringRef S, raw_ostream::Colors C) {
+  *ErrorOS << Argv0 + ": ";
+  if (Config->ColorDiagnostics) {
+    ErrorOS->changeColor(C, true);
+    *ErrorOS << S;
+    ErrorOS->resetColor();
+  } else {
+    *ErrorOS << S;
+  }
+}
 
-void log(const Twine &Msg) {
+void elf::log(const Twine &Msg) {
+  std::lock_guard<std::mutex> Lock(Mu);
   if (Config->Verbose)
-    outs() << Msg << "\n";
+    outs() << Argv0 << ": " << Msg << "\n";
 }
 
-void warning(const Twine &Msg) {
-  if (Config->FatalWarnings)
+void elf::warn(const Twine &Msg) {
+  if (Config->FatalWarnings) {
     error(Msg);
-  else
-    *ErrorOS << Msg << "\n";
+    return;
+  }
+  std::lock_guard<std::mutex> Lock(Mu);
+  print("warning: ", raw_ostream::MAGENTA);
+  *ErrorOS << Msg << "\n";
 }
 
-void error(const Twine &Msg) {
-  *ErrorOS << Msg << "\n";
-  HasError = true;
+void elf::error(const Twine &Msg) {
+  std::lock_guard<std::mutex> Lock(Mu);
+
+  if (Config->ErrorLimit == 0 || ErrorCount < Config->ErrorLimit) {
+    print("error: ", raw_ostream::RED);
+    *ErrorOS << Msg << "\n";
+  } else if (ErrorCount == Config->ErrorLimit) {
+    print("error: ", raw_ostream::RED);
+    *ErrorOS << "too many errors emitted, stopping now"
+             << " (use -error-limit=0 to see all errors)\n";
+    if (Config->ExitEarly)
+      exitLld(1);
+  }
+
+  ++ErrorCount;
 }
 
-void error(std::error_code EC, const Twine &Prefix) {
+void elf::error(std::error_code EC, const Twine &Prefix) {
   error(Prefix + ": " + EC.message());
 }
 
-void fatal(const Twine &Msg) {
-  *ErrorOS << Msg << "\n";
-  exit(1);
-}
+void elf::exitLld(int Val) {
+  // Dealloc/destroy ManagedStatic variables before calling
+  // _exit(). In a non-LTO build, this is a nop. In an LTO
+  // build allows us to get the output of -time-passes.
+  llvm_shutdown();
 
-void fatal(const Twine &Msg, const Twine &Prefix) {
-  fatal(Prefix + ": " + Msg);
+  outs().flush();
+  errs().flush();
+  _exit(Val);
 }
 
-void check(std::error_code EC) {
-  if (EC)
-    fatal(EC.message());
+void elf::fatal(const Twine &Msg) {
+  std::lock_guard<std::mutex> Lock(Mu);
+  print("error: ", raw_ostream::RED);
+  *ErrorOS << Msg << "\n";
+  exitLld(1);
 }
 
-void check(Error Err) {
-  check(errorToErrorCode(std::move(Err)));
+void elf::fatal(std::error_code EC, const Twine &Prefix) {
+  fatal(Prefix + ": " + EC.message());
 }
 
-} // namespace elf
 } // namespace lld
diff --git a/ELF/Error.h b/ELF/Error.h
index 552f50498464..1ec683595cf4 100644
--- a/ELF/Error.h
+++ b/ELF/Error.h
@@ -6,31 +6,47 @@
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
+//
+// In LLD, we have three levels of errors: fatal, error or warn.
+//
+// Fatal makes the program exit immediately with an error message.
+// You shouldn't use it except for reporting a corrupted input file.
+//
+// Error prints out an error message and increment a global variable
+// ErrorCount to record the fact that we met an error condition. It does
+// not exit, so it is safe for a lld-as-a-library use case. It is generally
+// useful because it can report more than one errors in a single run.
+//
+// Warn doesn't do anything but printing out a given message.
+//
+//===----------------------------------------------------------------------===//
 
-#ifndef LLD_COFF_ERROR_H
-#define LLD_COFF_ERROR_H
+#ifndef LLD_ELF_ERROR_H
+#define LLD_ELF_ERROR_H
 
 #include "lld/Core/LLVM.h"
 
+#include "llvm/Support/Error.h"
+
 namespace lld {
 namespace elf {
 
-extern bool HasError;
+extern uint64_t ErrorCount;
 extern llvm::raw_ostream *ErrorOS;
+extern llvm::StringRef Argv0;
 
 void log(const Twine &Msg);
-void warning(const Twine &Msg);
+void warn(const Twine &Msg);
 
 void error(const Twine &Msg);
 void error(std::error_code EC, const Twine &Prefix);
 
-template <typename T> void error(const ErrorOr<T> &V, const Twine &Prefix) {
-  error(V.getError(), Prefix);
-}
-
+LLVM_ATTRIBUTE_NORETURN void exitLld(int Val);
 LLVM_ATTRIBUTE_NORETURN void fatal(const Twine &Msg);
-LLVM_ATTRIBUTE_NORETURN void fatal(const Twine &Msg, const Twine &Prefix);
+LLVM_ATTRIBUTE_NORETURN void fatal(std::error_code EC, const Twine &Prefix);
 
+// check() functions are convenient functions to strip errors
+// from error-or-value objects.
 template <class T> T check(ErrorOr<T> E) {
   if (auto EC = E.getError())
     fatal(EC.message());
@@ -39,19 +55,23 @@ template <class T> T check(ErrorOr<T> E) {
 
 template <class T> T check(Expected<T> E) {
   if (!E)
-    fatal(errorToErrorCode(E.takeError()).message());
+    handleAllErrors(std::move(E.takeError()),
+                    [](llvm::ErrorInfoBase &EIB) -> Error {
+                      fatal(EIB.message());
+                      return Error::success();
+                    });
   return std::move(*E);
 }
 
 template <class T> T check(ErrorOr<T> E, const Twine &Prefix) {
   if (auto EC = E.getError())
-    fatal(EC.message(), Prefix);
+    fatal(Prefix + ": " + EC.message());
   return std::move(*E);
 }
 
 template <class T> T check(Expected<T> E, const Twine &Prefix) {
   if (!E)
-    fatal(errorToErrorCode(E.takeError()).message(), Prefix);
+    fatal(Prefix + ": " + errorToErrorCode(E.takeError()).message());
   return std::move(*E);
 }
 
diff --git a/ELF/GdbIndex.cpp b/ELF/GdbIndex.cpp
new file mode 100644
index 000000000000..762144dd0a96
--- /dev/null
+++ b/ELF/GdbIndex.cpp
@@ -0,0 +1,205 @@
+//===- GdbIndex.cpp -------------------------------------------------------===//
+//
+//                             The LLVM Linker
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// File contains classes for implementation of --gdb-index command line option.
+//
+// If that option is used, linker should emit a .gdb_index section that allows
+// debugger to locate and read .dwo files, containing neccessary debug
+// information.
+// More information about implementation can be found in DWARF specification,
+// latest version is available at http://dwarfstd.org.
+//
+// .gdb_index section format:
+//  (Information is based on/taken from
+//  https://sourceware.org/gdb/onlinedocs/gdb/Index-Section-Format.html (*))
+//
+// A mapped index consists of several areas, laid out in order:
+// 1) The file header.
+// 2) "The CU (compilation unit) list. This is a sequence of pairs of 64-bit
+//    little-endian values, sorted by the CU offset. The first element in each
+//    pair is the offset of a CU in the .debug_info section. The second element
+//    in each pair is the length of that CU. References to a CU elsewhere in the
+//    map are done using a CU index, which is just the 0-based index into this
+//    table. Note that if there are type CUs, then conceptually CUs and type CUs
+//    form a single list for the purposes of CU indices."(*)
+// 3) The types CU list. Depricated as .debug_types does not appear in the DWARF
+//    v5 specification.
+// 4) The address area. The address area is a sequence of address
+//    entries, where each entrie contains low address, high address and CU
+//    index.
+// 5) "The symbol table. This is an open-addressed hash table. The size of the
+//    hash table is always a power of 2. Each slot in the hash table consists of
+//    a pair of offset_type values. The first value is the offset of the
+//    symbol's name in the constant pool. The second value is the offset of the
+//    CU vector in the constant pool."(*)
+// 6) "The constant pool. This is simply a bunch of bytes. It is organized so
+//    that alignment is correct: CU vectors are stored first, followed by
+//    strings." (*)
+//
+// For constructing the .gdb_index section following steps should be performed:
+// 1) For file header nothing special should be done. It contains the offsets to
+//    the areas below.
+// 2) Scan the compilation unit headers of the .debug_info sections to build a
+//    list of compilation units.
+// 3) CU Types are no longer needed as DWARF skeleton type units never made it
+//    into the standard. lld does nothing to support parsing of .debug_types
+//    and generates empty types CU area in .gdb_index section.
+// 4) Address area entries are extracted from DW_TAG_compile_unit DIEs of
+//   .debug_info sections.
+// 5) For building the symbol table linker extracts the public names from the
+//   .debug_gnu_pubnames and .debug_gnu_pubtypes sections. Then it builds the
+//   hashtable in according to .gdb_index format specification.
+// 6) Constant pool is populated at the same time as symbol table.
+//===----------------------------------------------------------------------===//
+
+#include "GdbIndex.h"
+#include "llvm/DebugInfo/DWARF/DWARFDebugPubTable.h"
+#include "llvm/Object/ELFObjectFile.h"
+
+using namespace llvm;
+using namespace llvm::object;
+using namespace lld::elf;
+
+template <class ELFT>
+GdbIndexBuilder<ELFT>::GdbIndexBuilder(InputSection<ELFT> *DebugInfoSec)
+    : DebugInfoSec(DebugInfoSec) {
+  if (Expected<std::unique_ptr<object::ObjectFile>> Obj =
+          object::ObjectFile::createObjectFile(DebugInfoSec->getFile()->MB))
+    Dwarf.reset(new DWARFContextInMemory(*Obj.get(), this));
+  else
+    error(toString(DebugInfoSec->getFile()) + ": error creating DWARF context");
+}
+
+template <class ELFT>
+std::vector<std::pair<typename ELFT::uint, typename ELFT::uint>>
+GdbIndexBuilder<ELFT>::readCUList() {
+  std::vector<std::pair<uintX_t, uintX_t>> Ret;
+  for (std::unique_ptr<DWARFCompileUnit> &CU : Dwarf->compile_units())
+    Ret.push_back(
+        {DebugInfoSec->OutSecOff + CU->getOffset(), CU->getLength() + 4});
+  return Ret;
+}
+
+template <class ELFT>
+std::vector<std::pair<StringRef, uint8_t>>
+GdbIndexBuilder<ELFT>::readPubNamesAndTypes() {
+  const bool IsLE = ELFT::TargetEndianness == llvm::support::little;
+  StringRef Data[] = {Dwarf->getGnuPubNamesSection(),
+                      Dwarf->getGnuPubTypesSection()};
+
+  std::vector<std::pair<StringRef, uint8_t>> Ret;
+  for (StringRef D : Data) {
+    DWARFDebugPubTable PubTable(D, IsLE, true);
+    for (const DWARFDebugPubTable::Set &S : PubTable.getData())
+      for (const DWARFDebugPubTable::Entry &E : S.Entries)
+        Ret.push_back({E.Name, E.Descriptor.toBits()});
+  }
+  return Ret;
+}
+
+std::pair<bool, GdbSymbol *> GdbHashTab::add(uint32_t Hash, size_t Offset) {
+  if (Size * 4 / 3 >= Table.size())
+    expand();
+
+  GdbSymbol **Slot = findSlot(Hash, Offset);
+  bool New = false;
+  if (*Slot == nullptr) {
+    ++Size;
+    *Slot = new (Alloc) GdbSymbol(Hash, Offset);
+    New = true;
+  }
+  return {New, *Slot};
+}
+
+void GdbHashTab::expand() {
+  if (Table.empty()) {
+    Table.resize(InitialSize);
+    return;
+  }
+  std::vector<GdbSymbol *> NewTable(Table.size() * 2);
+  NewTable.swap(Table);
+
+  for (GdbSymbol *Sym : NewTable) {
+    if (!Sym)
+      continue;
+    GdbSymbol **Slot = findSlot(Sym->NameHash, Sym->NameOffset);
+    *Slot = Sym;
+  }
+}
+
+// Methods finds a slot for symbol with given hash. The step size used to find
+// the next candidate slot when handling a hash collision is specified in
+// .gdb_index section format. The hash value for a table entry is computed by
+// applying an iterative hash function to the symbol's name.
+GdbSymbol **GdbHashTab::findSlot(uint32_t Hash, size_t Offset) {
+  uint32_t Index = Hash & (Table.size() - 1);
+  uint32_t Step = ((Hash * 17) & (Table.size() - 1)) | 1;
+
+  for (;;) {
+    GdbSymbol *S = Table[Index];
+    if (!S || ((S->NameOffset == Offset) && (S->NameHash == Hash)))
+      return &Table[Index];
+    Index = (Index + Step) & (Table.size() - 1);
+  }
+}
+
+template <class ELFT>
+static InputSectionBase<ELFT> *
+findSection(ArrayRef<InputSectionBase<ELFT> *> Arr, uint64_t Offset) {
+  for (InputSectionBase<ELFT> *S : Arr)
+    if (S && S != &InputSection<ELFT>::Discarded)
+      if (Offset >= S->Offset && Offset < S->Offset + S->getSize())
+        return S;
+  return nullptr;
+}
+
+template <class ELFT>
+std::vector<AddressEntry<ELFT>>
+GdbIndexBuilder<ELFT>::readAddressArea(size_t CurrentCU) {
+  std::vector<AddressEntry<ELFT>> Ret;
+  for (const auto &CU : Dwarf->compile_units()) {
+    DWARFAddressRangesVector Ranges;
+    CU->collectAddressRanges(Ranges);
+
+    ArrayRef<InputSectionBase<ELFT> *> Sections =
+        DebugInfoSec->getFile()->getSections();
+
+    for (std::pair<uint64_t, uint64_t> &R : Ranges)
+      if (InputSectionBase<ELFT> *S = findSection(Sections, R.first))
+        Ret.push_back(
+            {S, R.first - S->Offset, R.second - S->Offset, CurrentCU});
+    ++CurrentCU;
+  }
+  return Ret;
+}
+
+// We return file offset as load address for allocatable sections. That is
+// currently used for collecting address ranges in readAddressArea(). We are
+// able then to find section index that range belongs to.
+template <class ELFT>
+uint64_t GdbIndexBuilder<ELFT>::getSectionLoadAddress(
+    const object::SectionRef &Sec) const {
+  if (static_cast<const ELFSectionRef &>(Sec).getFlags() & ELF::SHF_ALLOC)
+    return static_cast<const ELFSectionRef &>(Sec).getOffset();
+  return 0;
+}
+
+template <class ELFT>
+std::unique_ptr<LoadedObjectInfo> GdbIndexBuilder<ELFT>::clone() const {
+  return {};
+}
+
+namespace lld {
+namespace elf {
+template class GdbIndexBuilder<ELF32LE>;
+template class GdbIndexBuilder<ELF32BE>;
+template class GdbIndexBuilder<ELF64LE>;
+template class GdbIndexBuilder<ELF64BE>;
+}
+}
diff --git a/ELF/GdbIndex.h b/ELF/GdbIndex.h
new file mode 100644
index 000000000000..c761ea173a8d
--- /dev/null
+++ b/ELF/GdbIndex.h
@@ -0,0 +1,99 @@
+//===- GdbIndex.h --------------------------------------------*- C++ -*-===//
+//
+//                             The LLVM Linker
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===-------------------------------------------------------------------===//
+
+#ifndef LLD_ELF_GDB_INDEX_H
+#define LLD_ELF_GDB_INDEX_H
+
+#include "InputFiles.h"
+#include "llvm/Object/ELF.h"
+#include "llvm/DebugInfo/DWARF/DWARFContext.h"
+
+namespace lld {
+namespace elf {
+
+template <class ELFT> class InputSection;
+
+// Struct represents single entry of address area of gdb index.
+template <class ELFT> struct AddressEntry {
+  InputSectionBase<ELFT> *Section;
+  uint64_t LowAddress;
+  uint64_t HighAddress;
+  size_t CuIndex;
+};
+
+// GdbIndexBuilder is a helper class used for extracting data required
+// for building .gdb_index section from objects.
+template <class ELFT> class GdbIndexBuilder : public llvm::LoadedObjectInfo {
+  typedef typename ELFT::uint uintX_t;
+
+  InputSection<ELFT> *DebugInfoSec;
+
+  std::unique_ptr<llvm::DWARFContext> Dwarf;
+
+public:
+  GdbIndexBuilder(InputSection<ELFT> *DebugInfoSec);
+
+  // Extracts the compilation units. Each first element of pair is a offset of a
+  // CU in the .debug_info section and second is the length of that CU.
+  std::vector<std::pair<uintX_t, uintX_t>> readCUList();
+
+  // Extracts the vector of address area entries. Accepts global index of last
+  // parsed CU.
+  std::vector<AddressEntry<ELFT>> readAddressArea(size_t CurrentCU);
+
+  // Method extracts public names and types. It returns list of name and
+  // gnu_pub* kind pairs.
+  std::vector<std::pair<StringRef, uint8_t>> readPubNamesAndTypes();
+
+private:
+  // Method returns section file offset as a load addres for DWARF parser. That
+  // allows to find the target section index for address ranges.
+  uint64_t
+  getSectionLoadAddress(const llvm::object::SectionRef &Sec) const override;
+  std::unique_ptr<llvm::LoadedObjectInfo> clone() const override;
+};
+
+// Element of GdbHashTab hash table.
+struct GdbSymbol {
+  GdbSymbol(uint32_t Hash, size_t Offset)
+      : NameHash(Hash), NameOffset(Offset) {}
+  uint32_t NameHash;
+  size_t NameOffset;
+  size_t CuVectorIndex;
+};
+
+// This class manages the hashed symbol table for the .gdb_index section.
+// The hash value for a table entry is computed by applying an iterative hash
+// function to the symbol's name.
+class GdbHashTab final {
+public:
+  std::pair<bool, GdbSymbol *> add(uint32_t Hash, size_t Offset);
+
+  size_t getCapacity() { return Table.size(); }
+  GdbSymbol *getSymbol(size_t I) { return Table[I]; }
+
+private:
+  void expand();
+
+  GdbSymbol **findSlot(uint32_t Hash, size_t Offset);
+
+  llvm::BumpPtrAllocator Alloc;
+  std::vector<GdbSymbol *> Table;
+
+  // Size keeps the amount of filled entries in Table.
+  size_t Size = 0;
+
+  // Initial size must be a power of 2.
+  static const int32_t InitialSize = 1024;
+};
+
+} // namespace elf
+} // namespace lld
+
+#endif
diff --git a/ELF/ICF.cpp b/ELF/ICF.cpp
index 10a2603b3b3e..32cd0f8a185c 100644
--- a/ELF/ICF.cpp
+++ b/ELF/ICF.cpp
@@ -7,63 +7,82 @@
 //
 //===----------------------------------------------------------------------===//
 //
-// Identical Code Folding is a feature to merge sections not by name (which
-// is regular comdat handling) but by contents. If two non-writable sections
-// have the same data, relocations, attributes, etc., then the two
-// are considered identical and merged by the linker. This optimization
-// makes outputs smaller.
+// ICF is short for Identical Code Folding. This is a size optimization to
+// identify and merge two or more read-only sections (typically functions)
+// that happened to have the same contents. It usually reduces output size
+// by a few percent.
 //
-// ICF is theoretically a problem of reducing graphs by merging as many
-// identical subgraphs as possible if we consider sections as vertices and
-// relocations as edges. It may sound simple, but it is a bit more
-// complicated than you might think. The order of processing sections
-// matters because merging two sections can make other sections, whose
-// relocations now point to the same section, mergeable. Graphs may contain
-// cycles. We need a sophisticated algorithm to do this properly and
-// efficiently.
+// In ICF, two sections are considered identical if they have the same
+// section flags, section data, and relocations. Relocations are tricky,
+// because two relocations are considered the same if they have the same
+// relocation types, values, and if they point to the same sections *in
+// terms of ICF*.
 //
-// What we do in this file is this. We split sections into groups. Sections
-// in the same group are considered identical.
+// Here is an example. If foo and bar defined below are compiled to the
+// same machine instructions, ICF can and should merge the two, although
+// their relocations point to each other.
 //
-// We begin by optimistically putting all sections into a single equivalence
-// class. Then we apply a series of checks that split this initial
-// equivalence class into more and more refined equivalence classes based on
-// the properties by which a section can be distinguished.
+//   void foo() { bar(); }
+//   void bar() { foo(); }
 //
-// We begin by checking that the section contents and flags are the
-// same. This only needs to be done once since these properties don't depend
-// on the current equivalence class assignment.
+// If you merge the two, their relocations point to the same section and
+// thus you know they are mergeable, but how do you know they are
+// mergeable in the first place? This is not an easy problem to solve.
 //
-// Then we split the equivalence classes based on checking that their
-// relocations are the same, where relocation targets are compared by their
-// equivalence class, not the concrete section. This may need to be done
-// multiple times because as the equivalence classes are refined, two
-// sections that had a relocation target in the same equivalence class may
-// now target different equivalence classes, and hence these two sections
-// must be put in different equivalence classes (whereas in the previous
-// iteration they were not since the relocation target was the same.)
+// What we are doing in LLD is to partition sections into equivalence
+// classes. Sections in the same equivalence class when the algorithm
+// terminates are considered identical. Here are details:
 //
-// Our algorithm is smart enough to merge the following mutually-recursive
-// functions.
+// 1. First, we partition sections using their hash values as keys. Hash
+//    values contain section types, section contents and numbers of
+//    relocations. During this step, relocation targets are not taken into
+//    account. We just put sections that apparently differ into different
+//    equivalence classes.
 //
-//   void foo() { bar(); }
-//   void bar() { foo(); }
+// 2. Next, for each equivalence class, we visit sections to compare
+//    relocation targets. Relocation targets are considered equivalent if
+//    their targets are in the same equivalence class. Sections with
+//    different relocation targets are put into different equivalence
+//    clases.
+//
+// 3. If we split an equivalence class in step 2, two relocations
+//    previously target the same equivalence class may now target
+//    different equivalence classes. Therefore, we repeat step 2 until a
+//    convergence is obtained.
+//
+// 4. For each equivalence class C, pick an arbitrary section in C, and
+//    merge all the other sections in C with it.
+//
+// For small programs, this algorithm needs 3-5 iterations. For large
+// programs such as Chromium, it takes more than 20 iterations.
+//
+// This algorithm was mentioned as an "optimistic algorithm" in [1],
+// though gold implements a different algorithm than this.
+//
+// We parallelize each step so that multiple threads can work on different
+// equivalence classes concurrently. That gave us a large performance
+// boost when applying ICF on large programs. For example, MSVC link.exe
+// or GNU gold takes 10-20 seconds to apply ICF on Chromium, whose output
+// size is about 1.5 GB, but LLD can finish it in less than 2 seconds on a
+// 2.8 GHz 40 core machine. Even without threading, LLD's ICF is still
+// faster than MSVC or gold though.
 //
-// This algorithm is so-called "optimistic" algorithm described in
-// http://research.google.com/pubs/pub36912.html. (Note that what GNU
-// gold implemented is different from the optimistic algorithm.)
+// [1] Safe ICF: Pointer Safe and Unwinding aware Identical Code Folding
+// in the Gold Linker
+// http://static.googleusercontent.com/media/research.google.com/en//pubs/archive/36912.pdf
 //
 //===----------------------------------------------------------------------===//
 
 #include "ICF.h"
 #include "Config.h"
-#include "OutputSections.h"
 #include "SymbolTable.h"
+#include "Threads.h"
 
 #include "llvm/ADT/Hashing.h"
 #include "llvm/Object/ELF.h"
 #include "llvm/Support/ELF.h"
-#include "llvm/Support/raw_ostream.h"
+#include <algorithm>
+#include <atomic>
 
 using namespace lld;
 using namespace lld::elf;
@@ -71,143 +90,132 @@ using namespace llvm;
 using namespace llvm::ELF;
 using namespace llvm::object;
 
-namespace lld {
-namespace elf {
+namespace {
 template <class ELFT> class ICF {
-  typedef typename ELFT::Shdr Elf_Shdr;
-  typedef typename ELFT::Sym Elf_Sym;
-  typedef typename ELFT::uint uintX_t;
-  typedef Elf_Rel_Impl<ELFT, false> Elf_Rel;
-
-  using Comparator = std::function<bool(const InputSection<ELFT> *,
-                                        const InputSection<ELFT> *)>;
-
 public:
   void run();
 
 private:
-  uint64_t NextId = 1;
-
-  static void setLive(SymbolTable<ELFT> *S);
-  static uint64_t relSize(InputSection<ELFT> *S);
-  static uint64_t getHash(InputSection<ELFT> *S);
-  static bool isEligible(InputSectionBase<ELFT> *Sec);
-  static std::vector<InputSection<ELFT> *> getSections();
-
-  void segregate(InputSection<ELFT> **Begin, InputSection<ELFT> **End,
-                 Comparator Eq);
-
-  void forEachGroup(std::vector<InputSection<ELFT> *> &V, Comparator Eq);
+  void segregate(size_t Begin, size_t End, bool Constant);
 
   template <class RelTy>
-  static bool relocationEq(ArrayRef<RelTy> RA, ArrayRef<RelTy> RB);
+  bool constantEq(ArrayRef<RelTy> RelsA, ArrayRef<RelTy> RelsB);
 
   template <class RelTy>
-  static bool variableEq(const InputSection<ELFT> *A,
-                         const InputSection<ELFT> *B, ArrayRef<RelTy> RA,
-                         ArrayRef<RelTy> RB);
-
-  static bool equalsConstant(const InputSection<ELFT> *A,
-                             const InputSection<ELFT> *B);
-
-  static bool equalsVariable(const InputSection<ELFT> *A,
-                             const InputSection<ELFT> *B);
+  bool variableEq(const InputSection<ELFT> *A, ArrayRef<RelTy> RelsA,
+                  const InputSection<ELFT> *B, ArrayRef<RelTy> RelsB);
+
+  bool equalsConstant(const InputSection<ELFT> *A, const InputSection<ELFT> *B);
+  bool equalsVariable(const InputSection<ELFT> *A, const InputSection<ELFT> *B);
+
+  size_t findBoundary(size_t Begin, size_t End);
+
+  void forEachClassRange(size_t Begin, size_t End,
+                         std::function<void(size_t, size_t)> Fn);
+
+  void forEachClass(std::function<void(size_t, size_t)> Fn);
+
+  std::vector<InputSection<ELFT> *> Sections;
+
+  // We repeat the main loop while `Repeat` is true.
+  std::atomic<bool> Repeat;
+
+  // The main loop counter.
+  int Cnt = 0;
+
+  // We have two locations for equivalence classes. On the first iteration
+  // of the main loop, Class[0] has a valid value, and Class[1] contains
+  // garbage. We read equivalence classes from slot 0 and write to slot 1.
+  // So, Class[0] represents the current class, and Class[1] represents
+  // the next class. On each iteration, we switch their roles and use them
+  // alternately.
+  //
+  // Why are we doing this? Recall that other threads may be working on
+  // other equivalence classes in parallel. They may read sections that we
+  // are updating. We cannot update equivalence classes in place because
+  // it breaks the invariance that all possibly-identical sections must be
+  // in the same equivalence class at any moment. In other words, the for
+  // loop to update equivalence classes is not atomic, and that is
+  // observable from other threads. By writing new classes to other
+  // places, we can keep the invariance.
+  //
+  // Below, `Current` has the index of the current class, and `Next` has
+  // the index of the next class. If threading is enabled, they are either
+  // (0, 1) or (1, 0).
+  //
+  // Note on single-thread: if that's the case, they are always (0, 0)
+  // because we can safely read the next class without worrying about race
+  // conditions. Using the same location makes this algorithm converge
+  // faster because it uses results of the same iteration earlier.
+  int Current = 0;
+  int Next = 0;
 };
 }
-}
 
 // Returns a hash value for S. Note that the information about
 // relocation targets is not included in the hash value.
-template <class ELFT> uint64_t ICF<ELFT>::getHash(InputSection<ELFT> *S) {
-  uint64_t Flags = S->getSectionHdr()->sh_flags;
-  uint64_t H = hash_combine(Flags, S->getSize());
-  for (const Elf_Shdr *Rel : S->RelocSections)
-    H = hash_combine(H, (uint64_t)Rel->sh_size);
-  return H;
+template <class ELFT> static uint32_t getHash(InputSection<ELFT> *S) {
+  return hash_combine(S->Flags, S->getSize(), S->NumRelocations);
 }
 
-// Returns true if Sec is subject of ICF.
-template <class ELFT> bool ICF<ELFT>::isEligible(InputSectionBase<ELFT> *Sec) {
-  if (!Sec || Sec == &InputSection<ELFT>::Discarded || !Sec->Live)
-    return false;
-  auto *S = dyn_cast<InputSection<ELFT>>(Sec);
-  if (!S)
-    return false;
-
+// Returns true if section S is subject of ICF.
+template <class ELFT> static bool isEligible(InputSection<ELFT> *S) {
   // .init and .fini contains instructions that must be executed to
   // initialize and finalize the process. They cannot and should not
   // be merged.
-  StringRef Name = S->getSectionName();
-  if (Name == ".init" || Name == ".fini")
-    return false;
-
-  const Elf_Shdr &H = *S->getSectionHdr();
-  return (H.sh_flags & SHF_ALLOC) && (~H.sh_flags & SHF_WRITE);
-}
-
-template <class ELFT>
-std::vector<InputSection<ELFT> *> ICF<ELFT>::getSections() {
-  std::vector<InputSection<ELFT> *> V;
-  for (const std::unique_ptr<ObjectFile<ELFT>> &F :
-       Symtab<ELFT>::X->getObjectFiles())
-    for (InputSectionBase<ELFT> *S : F->getSections())
-      if (isEligible(S))
-        V.push_back(cast<InputSection<ELFT>>(S));
-  return V;
+  return S->Live && (S->Flags & SHF_ALLOC) && !(S->Flags & SHF_WRITE) &&
+         S->Name != ".init" && S->Name != ".fini";
 }
 
-// All sections between Begin and End must have the same group ID before
-// you call this function. This function compare sections between Begin
-// and End using Eq and assign new group IDs for new groups.
+// Split an equivalence class into smaller classes.
 template <class ELFT>
-void ICF<ELFT>::segregate(InputSection<ELFT> **Begin, InputSection<ELFT> **End,
-                          Comparator Eq) {
-  // This loop rearranges [Begin, End) so that all sections that are
-  // equal in terms of Eq are contiguous. The algorithm is quadratic in
-  // the worst case, but that is not an issue in practice because the
-  // number of distinct sections in [Begin, End) is usually very small.
-  InputSection<ELFT> **I = Begin;
-  for (;;) {
-    InputSection<ELFT> *Head = *I;
+void ICF<ELFT>::segregate(size_t Begin, size_t End, bool Constant) {
+  // This loop rearranges sections in [Begin, End) so that all sections
+  // that are equal in terms of equals{Constant,Variable} are contiguous
+  // in [Begin, End).
+  //
+  // The algorithm is quadratic in the worst case, but that is not an
+  // issue in practice because the number of the distinct sections in
+  // each range is usually very small.
+
+  while (Begin < End) {
+    // Divide [Begin, End) into two. Let Mid be the start index of the
+    // second group.
     auto Bound = std::stable_partition(
-        I + 1, End, [&](InputSection<ELFT> *S) { return Eq(Head, S); });
-    if (Bound == End)
-      return;
-    uint64_t Id = NextId++;
-    for (; I != Bound; ++I)
-      (*I)->GroupId = Id;
-  }
-}
-
-template <class ELFT>
-void ICF<ELFT>::forEachGroup(std::vector<InputSection<ELFT> *> &V,
-                             Comparator Eq) {
-  for (InputSection<ELFT> **I = V.data(), **E = I + V.size(); I != E;) {
-    InputSection<ELFT> *Head = *I;
-    auto Bound = std::find_if(I + 1, E, [&](InputSection<ELFT> *S) {
-      return S->GroupId != Head->GroupId;
-    });
-    segregate(I, Bound, Eq);
-    I = Bound;
+        Sections.begin() + Begin + 1, Sections.begin() + End,
+        [&](InputSection<ELFT> *S) {
+          if (Constant)
+            return equalsConstant(Sections[Begin], S);
+          return equalsVariable(Sections[Begin], S);
+        });
+    size_t Mid = Bound - Sections.begin();
+
+    // Now we split [Begin, End) into [Begin, Mid) and [Mid, End) by
+    // updating the sections in [Begin, End). We use Mid as an equivalence
+    // class ID because every group ends with a unique index.
+    for (size_t I = Begin; I < Mid; ++I)
+      Sections[I]->Class[Next] = Mid;
+
+    // If we created a group, we need to iterate the main loop again.
+    if (Mid != End)
+      Repeat = true;
+
+    Begin = Mid;
   }
 }
 
 // Compare two lists of relocations.
 template <class ELFT>
 template <class RelTy>
-bool ICF<ELFT>::relocationEq(ArrayRef<RelTy> RelsA, ArrayRef<RelTy> RelsB) {
-  const RelTy *IA = RelsA.begin();
-  const RelTy *EA = RelsA.end();
-  const RelTy *IB = RelsB.begin();
-  const RelTy *EB = RelsB.end();
-  if (EA - IA != EB - IB)
-    return false;
-  for (; IA != EA; ++IA, ++IB)
-    if (IA->r_offset != IB->r_offset ||
-        IA->getType(Config->Mips64EL) != IB->getType(Config->Mips64EL) ||
-        getAddend<ELFT>(*IA) != getAddend<ELFT>(*IB))
-      return false;
-  return true;
+bool ICF<ELFT>::constantEq(ArrayRef<RelTy> RelsA, ArrayRef<RelTy> RelsB) {
+  auto Eq = [](const RelTy &A, const RelTy &B) {
+    return A.r_offset == B.r_offset &&
+           A.getType(Config->Mips64EL) == B.getType(Config->Mips64EL) &&
+           getAddend<ELFT>(A) == getAddend<ELFT>(B);
+  };
+
+  return RelsA.size() == RelsB.size() &&
+         std::equal(RelsA.begin(), RelsA.end(), RelsB.begin(), Eq);
 }
 
 // Compare "non-moving" part of two InputSections, namely everything
@@ -215,125 +223,155 @@ bool ICF<ELFT>::relocationEq(ArrayRef<RelTy> RelsA, ArrayRef<RelTy> RelsB) {
 template <class ELFT>
 bool ICF<ELFT>::equalsConstant(const InputSection<ELFT> *A,
                                const InputSection<ELFT> *B) {
-  if (A->RelocSections.size() != B->RelocSections.size())
+  if (A->NumRelocations != B->NumRelocations || A->Flags != B->Flags ||
+      A->getSize() != B->getSize() || A->Data != B->Data)
     return false;
 
-  for (size_t I = 0, E = A->RelocSections.size(); I != E; ++I) {
-    const Elf_Shdr *RA = A->RelocSections[I];
-    const Elf_Shdr *RB = B->RelocSections[I];
-    ELFFile<ELFT> &FileA = A->File->getObj();
-    ELFFile<ELFT> &FileB = B->File->getObj();
-    if (RA->sh_type == SHT_RELA) {
-      if (!relocationEq(FileA.relas(RA), FileB.relas(RB)))
-        return false;
-    } else {
-      if (!relocationEq(FileA.rels(RA), FileB.rels(RB)))
-        return false;
-    }
-  }
-
-  return A->getSectionHdr()->sh_flags == B->getSectionHdr()->sh_flags &&
-         A->getSize() == B->getSize() &&
-         A->getSectionData() == B->getSectionData();
+  if (A->AreRelocsRela)
+    return constantEq(A->relas(), B->relas());
+  return constantEq(A->rels(), B->rels());
 }
 
+// Compare two lists of relocations. Returns true if all pairs of
+// relocations point to the same section in terms of ICF.
 template <class ELFT>
 template <class RelTy>
-bool ICF<ELFT>::variableEq(const InputSection<ELFT> *A,
-                           const InputSection<ELFT> *B, ArrayRef<RelTy> RelsA,
-                           ArrayRef<RelTy> RelsB) {
-  const RelTy *IA = RelsA.begin();
-  const RelTy *EA = RelsA.end();
-  const RelTy *IB = RelsB.begin();
-  for (; IA != EA; ++IA, ++IB) {
-    SymbolBody &SA = A->File->getRelocTargetSym(*IA);
-    SymbolBody &SB = B->File->getRelocTargetSym(*IB);
+bool ICF<ELFT>::variableEq(const InputSection<ELFT> *A, ArrayRef<RelTy> RelsA,
+                           const InputSection<ELFT> *B, ArrayRef<RelTy> RelsB) {
+  auto Eq = [&](const RelTy &RA, const RelTy &RB) {
+    // The two sections must be identical.
+    SymbolBody &SA = A->getFile()->getRelocTargetSym(RA);
+    SymbolBody &SB = B->getFile()->getRelocTargetSym(RB);
     if (&SA == &SB)
-      continue;
+      return true;
 
-    // Or, the symbols should be pointing to the same section
-    // in terms of the group ID.
+    // Or, the two sections must be in the same equivalence class.
     auto *DA = dyn_cast<DefinedRegular<ELFT>>(&SA);
     auto *DB = dyn_cast<DefinedRegular<ELFT>>(&SB);
     if (!DA || !DB)
       return false;
     if (DA->Value != DB->Value)
       return false;
-    InputSection<ELFT> *X = dyn_cast<InputSection<ELFT>>(DA->Section);
-    InputSection<ELFT> *Y = dyn_cast<InputSection<ELFT>>(DB->Section);
-    if (X && Y && X->GroupId && X->GroupId == Y->GroupId)
-      continue;
-    return false;
-  }
-  return true;
+
+    auto *X = dyn_cast<InputSection<ELFT>>(DA->Section);
+    auto *Y = dyn_cast<InputSection<ELFT>>(DB->Section);
+    if (!X || !Y)
+      return false;
+
+    // Ineligible sections are in the special equivalence class 0.
+    // They can never be the same in terms of the equivalence class.
+    if (X->Class[Current] == 0)
+      return false;
+
+    return X->Class[Current] == Y->Class[Current];
+  };
+
+  return std::equal(RelsA.begin(), RelsA.end(), RelsB.begin(), Eq);
 }
 
 // Compare "moving" part of two InputSections, namely relocation targets.
 template <class ELFT>
 bool ICF<ELFT>::equalsVariable(const InputSection<ELFT> *A,
                                const InputSection<ELFT> *B) {
-  for (size_t I = 0, E = A->RelocSections.size(); I != E; ++I) {
-    const Elf_Shdr *RA = A->RelocSections[I];
-    const Elf_Shdr *RB = B->RelocSections[I];
-    ELFFile<ELFT> &FileA = A->File->getObj();
-    ELFFile<ELFT> &FileB = B->File->getObj();
-    if (RA->sh_type == SHT_RELA) {
-      if (!variableEq(A, B, FileA.relas(RA), FileB.relas(RB)))
-        return false;
-    } else {
-      if (!variableEq(A, B, FileA.rels(RA), FileB.rels(RB)))
-        return false;
-    }
+  if (A->AreRelocsRela)
+    return variableEq(A, A->relas(), B, B->relas());
+  return variableEq(A, A->rels(), B, B->rels());
+}
+
+template <class ELFT> size_t ICF<ELFT>::findBoundary(size_t Begin, size_t End) {
+  uint32_t Class = Sections[Begin]->Class[Current];
+  for (size_t I = Begin + 1; I < End; ++I)
+    if (Class != Sections[I]->Class[Current])
+      return I;
+  return End;
+}
+
+// Sections in the same equivalence class are contiguous in Sections
+// vector. Therefore, Sections vector can be considered as contiguous
+// groups of sections, grouped by the class.
+//
+// This function calls Fn on every group that starts within [Begin, End).
+// Note that a group must starts in that range but doesn't necessarily
+// have to end before End.
+template <class ELFT>
+void ICF<ELFT>::forEachClassRange(size_t Begin, size_t End,
+                                  std::function<void(size_t, size_t)> Fn) {
+  if (Begin > 0)
+    Begin = findBoundary(Begin - 1, End);
+
+  while (Begin < End) {
+    size_t Mid = findBoundary(Begin, Sections.size());
+    Fn(Begin, Mid);
+    Begin = Mid;
   }
-  return true;
+}
+
+// Call Fn on each equivalence class.
+template <class ELFT>
+void ICF<ELFT>::forEachClass(std::function<void(size_t, size_t)> Fn) {
+  // If threading is disabled or the number of sections are
+  // too small to use threading, call Fn sequentially.
+  if (!Config->Threads || Sections.size() < 1024) {
+    forEachClassRange(0, Sections.size(), Fn);
+    ++Cnt;
+    return;
+  }
+
+  Current = Cnt % 2;
+  Next = (Cnt + 1) % 2;
+
+  // Split sections into 256 shards and call Fn in parallel.
+  size_t NumShards = 256;
+  size_t Step = Sections.size() / NumShards;
+  forLoop(0, NumShards,
+          [&](size_t I) { forEachClassRange(I * Step, (I + 1) * Step, Fn); });
+  forEachClassRange(Step * NumShards, Sections.size(), Fn);
+  ++Cnt;
 }
 
 // The main function of ICF.
 template <class ELFT> void ICF<ELFT>::run() {
-  // Initially, we use hash values as section group IDs. Therefore,
-  // if two sections have the same ID, they are likely (but not
-  // guaranteed) to have the same static contents in terms of ICF.
-  std::vector<InputSection<ELFT> *> V = getSections();
-  for (InputSection<ELFT> *S : V)
-    // Set MSB on to avoid collisions with serial group IDs
-    S->GroupId = getHash(S) | (uint64_t(1) << 63);
-
-  // From now on, sections in V are ordered so that sections in
-  // the same group are consecutive in the vector.
-  std::stable_sort(V.begin(), V.end(),
+  // Collect sections to merge.
+  for (InputSectionBase<ELFT> *Sec : Symtab<ELFT>::X->Sections)
+    if (auto *S = dyn_cast<InputSection<ELFT>>(Sec))
+      if (isEligible(S))
+        Sections.push_back(S);
+
+  // Initially, we use hash values to partition sections.
+  for (InputSection<ELFT> *S : Sections)
+    // Set MSB to 1 to avoid collisions with non-hash IDs.
+    S->Class[0] = getHash(S) | (1 << 31);
+
+  // From now on, sections in Sections vector are ordered so that sections
+  // in the same equivalence class are consecutive in the vector.
+  std::stable_sort(Sections.begin(), Sections.end(),
                    [](InputSection<ELFT> *A, InputSection<ELFT> *B) {
-                     return A->GroupId < B->GroupId;
+                     return A->Class[0] < B->Class[0];
                    });
 
   // Compare static contents and assign unique IDs for each static content.
-  forEachGroup(V, equalsConstant);
+  forEachClass([&](size_t Begin, size_t End) { segregate(Begin, End, true); });
 
-  // Split groups by comparing relocations until we get a convergence.
-  int Cnt = 1;
-  for (;;) {
-    ++Cnt;
-    uint64_t Id = NextId;
-    forEachGroup(V, equalsVariable);
-    if (Id == NextId)
-      break;
-  }
-  log("ICF needed " + Twine(Cnt) + " iterations.");
-
-  // Merge sections in the same group.
-  for (auto I = V.begin(), E = V.end(); I != E;) {
-    InputSection<ELFT> *Head = *I++;
-    auto Bound = std::find_if(I, E, [&](InputSection<ELFT> *S) {
-      return Head->GroupId != S->GroupId;
-    });
-    if (I == Bound)
-      continue;
-    log("selected " + Head->getSectionName());
-    while (I != Bound) {
-      InputSection<ELFT> *S = *I++;
-      log("  removed " + S->getSectionName());
-      Head->replace(S);
+  // Split groups by comparing relocations until convergence is obtained.
+  do {
+    Repeat = false;
+    forEachClass(
+        [&](size_t Begin, size_t End) { segregate(Begin, End, false); });
+  } while (Repeat);
+
+  log("ICF needed " + Twine(Cnt) + " iterations");
+
+  // Merge sections by the equivalence class.
+  forEachClass([&](size_t Begin, size_t End) {
+    if (End - Begin == 1)
+      return;
+
+    log("selected " + Sections[Begin]->Name);
+    for (size_t I = Begin + 1; I < End; ++I) {
+      log("  removed " + Sections[I]->Name);
+      Sections[Begin]->replace(Sections[I]);
     }
-  }
+  });
 }
 
 // ICF entry point function.
diff --git a/ELF/InputFiles.cpp b/ELF/InputFiles.cpp
index 426d9c39715d..2a8659921463 100644
--- a/ELF/InputFiles.cpp
+++ b/ELF/InputFiles.cpp
@@ -11,13 +11,20 @@
 #include "Driver.h"
 #include "Error.h"
 #include "InputSection.h"
+#include "LinkerScript.h"
+#include "Memory.h"
 #include "SymbolTable.h"
 #include "Symbols.h"
+#include "SyntheticSections.h"
 #include "llvm/ADT/STLExtras.h"
-#include "llvm/Bitcode/ReaderWriter.h"
+#include "llvm/Bitcode/BitcodeReader.h"
 #include "llvm/CodeGen/Analysis.h"
+#include "llvm/DebugInfo/DWARF/DWARFContext.h"
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/Module.h"
+#include "llvm/LTO/LTO.h"
+#include "llvm/MC/StringTableBuilder.h"
+#include "llvm/Object/ELFObjectFile.h"
 #include "llvm/Support/Path.h"
 #include "llvm/Support/raw_ostream.h"
 
@@ -29,8 +36,68 @@ using namespace llvm::sys::fs;
 using namespace lld;
 using namespace lld::elf;
 
+namespace {
+// In ELF object file all section addresses are zero. If we have multiple
+// .text sections (when using -ffunction-section or comdat group) then
+// LLVM DWARF parser will not be able to parse .debug_line correctly, unless
+// we assign each section some unique address. This callback method assigns
+// each section an address equal to its offset in ELF object file.
+class ObjectInfo : public LoadedObjectInfo {
+public:
+  uint64_t getSectionLoadAddress(const object::SectionRef &Sec) const override {
+    return static_cast<const ELFSectionRef &>(Sec).getOffset();
+  }
+  std::unique_ptr<LoadedObjectInfo> clone() const override {
+    return std::unique_ptr<LoadedObjectInfo>();
+  }
+};
+}
+
+template <class ELFT> void elf::ObjectFile<ELFT>::initializeDwarfLine() {
+  std::unique_ptr<object::ObjectFile> Obj =
+      check(object::ObjectFile::createObjectFile(this->MB),
+            "createObjectFile failed");
+
+  ObjectInfo ObjInfo;
+  DWARFContextInMemory Dwarf(*Obj, &ObjInfo);
+  DwarfLine.reset(new DWARFDebugLine(&Dwarf.getLineSection().Relocs));
+  DataExtractor LineData(Dwarf.getLineSection().Data,
+                         ELFT::TargetEndianness == support::little,
+                         ELFT::Is64Bits ? 8 : 4);
+
+  // The second parameter is offset in .debug_line section
+  // for compilation unit (CU) of interest. We have only one
+  // CU (object file), so offset is always 0.
+  DwarfLine->getOrParseLineTable(LineData, 0);
+}
+
+// Returns source line information for a given offset
+// using DWARF debug info.
+template <class ELFT>
+std::string elf::ObjectFile<ELFT>::getLineInfo(InputSectionBase<ELFT> *S,
+                                               uintX_t Offset) {
+  if (!DwarfLine)
+    initializeDwarfLine();
+
+  // The offset to CU is 0.
+  const DWARFDebugLine::LineTable *Tbl = DwarfLine->getLineTable(0);
+  if (!Tbl)
+    return "";
+
+  // Use fake address calcuated by adding section file offset and offset in
+  // section. See comments for ObjectInfo class.
+  DILineInfo Info;
+  Tbl->getFileLineInfoForAddress(
+      S->Offset + Offset, nullptr,
+      DILineInfoSpecifier::FileLineInfoKind::AbsoluteFilePath, Info);
+  if (Info.Line == 0)
+    return "";
+  return convertToUnixPathSeparator(Info.FileName) + ":" +
+         std::to_string(Info.Line);
+}
+
 // Returns "(internal)", "foo.a(bar.o)" or "baz.o".
-std::string elf::getFilename(const InputFile *F) {
+std::string elf::toString(const InputFile *F) {
   if (!F)
     return "(internal)";
   if (!F->ArchiveName.empty())
@@ -38,15 +105,6 @@ std::string elf::getFilename(const InputFile *F) {
   return F->getName();
 }
 
-template <class ELFT>
-static ELFFile<ELFT> createELFObj(MemoryBufferRef MB) {
-  std::error_code EC;
-  ELFFile<ELFT> F(MB.getBuffer(), EC);
-  if (EC)
-    error(EC, "failed to read " + MB.getBufferIdentifier());
-  return F;
-}
-
 template <class ELFT> static ELFKind getELFKind() {
   if (ELFT::TargetEndianness == support::little)
     return ELFT::Is64Bits ? ELF64LEKind : ELF32LEKind;
@@ -54,41 +112,31 @@ template <class ELFT> static ELFKind getELFKind() {
 }
 
 template <class ELFT>
-ELFFileBase<ELFT>::ELFFileBase(Kind K, MemoryBufferRef MB)
-    : InputFile(K, MB), ELFObj(createELFObj<ELFT>(MB)) {
+ELFFileBase<ELFT>::ELFFileBase(Kind K, MemoryBufferRef MB) : InputFile(K, MB) {
   EKind = getELFKind<ELFT>();
-  EMachine = ELFObj.getHeader()->e_machine;
+  EMachine = getObj().getHeader()->e_machine;
+  OSABI = getObj().getHeader()->e_ident[llvm::ELF::EI_OSABI];
 }
 
 template <class ELFT>
-typename ELFT::SymRange ELFFileBase<ELFT>::getElfSymbols(bool OnlyGlobals) {
-  if (!Symtab)
-    return Elf_Sym_Range(nullptr, nullptr);
-  Elf_Sym_Range Syms = ELFObj.symbols(Symtab);
-  uint32_t NumSymbols = std::distance(Syms.begin(), Syms.end());
-  uint32_t FirstNonLocal = Symtab->sh_info;
-  if (FirstNonLocal > NumSymbols)
-    fatal(getFilename(this) + ": invalid sh_info in symbol table");
-
-  if (OnlyGlobals)
-    return makeArrayRef(Syms.begin() + FirstNonLocal, Syms.end());
-  return makeArrayRef(Syms.begin(), Syms.end());
+typename ELFT::SymRange ELFFileBase<ELFT>::getGlobalSymbols() {
+  return makeArrayRef(Symbols.begin() + FirstNonLocal, Symbols.end());
 }
 
 template <class ELFT>
 uint32_t ELFFileBase<ELFT>::getSectionIndex(const Elf_Sym &Sym) const {
-  uint32_t I = Sym.st_shndx;
-  if (I == ELF::SHN_XINDEX)
-    return ELFObj.getExtendedSymbolTableIndex(&Sym, Symtab, SymtabSHNDX);
-  if (I >= ELF::SHN_LORESERVE)
-    return 0;
-  return I;
+  return check(getObj().getSectionIndex(&Sym, Symbols, SymtabSHNDX));
 }
 
-template <class ELFT> void ELFFileBase<ELFT>::initStringTable() {
-  if (!Symtab)
-    return;
-  StringTable = check(ELFObj.getStringTableForSymtab(*Symtab));
+template <class ELFT>
+void ELFFileBase<ELFT>::initSymtab(ArrayRef<Elf_Shdr> Sections,
+                                   const Elf_Shdr *Symtab) {
+  FirstNonLocal = Symtab->sh_info;
+  Symbols = check(getObj().symbols(Symtab));
+  if (FirstNonLocal == 0 || FirstNonLocal > Symbols.size())
+    fatal(toString(this) + ": invalid sh_info in symbol table");
+
+  StringTable = check(getObj().getStringTableForSymtab(*Symtab, Sections));
 }
 
 template <class ELFT>
@@ -97,37 +145,25 @@ elf::ObjectFile<ELFT>::ObjectFile(MemoryBufferRef M)
 
 template <class ELFT>
 ArrayRef<SymbolBody *> elf::ObjectFile<ELFT>::getNonLocalSymbols() {
-  if (!this->Symtab)
-    return this->SymbolBodies;
-  uint32_t FirstNonLocal = this->Symtab->sh_info;
-  return makeArrayRef(this->SymbolBodies).slice(FirstNonLocal);
+  return makeArrayRef(this->SymbolBodies).slice(this->FirstNonLocal);
 }
 
 template <class ELFT>
 ArrayRef<SymbolBody *> elf::ObjectFile<ELFT>::getLocalSymbols() {
-  if (!this->Symtab)
+  if (this->SymbolBodies.empty())
     return this->SymbolBodies;
-  uint32_t FirstNonLocal = this->Symtab->sh_info;
-  return makeArrayRef(this->SymbolBodies).slice(1, FirstNonLocal - 1);
+  return makeArrayRef(this->SymbolBodies).slice(1, this->FirstNonLocal - 1);
 }
 
 template <class ELFT>
 ArrayRef<SymbolBody *> elf::ObjectFile<ELFT>::getSymbols() {
-  if (!this->Symtab)
+  if (this->SymbolBodies.empty())
     return this->SymbolBodies;
   return makeArrayRef(this->SymbolBodies).slice(1);
 }
 
-template <class ELFT> uint32_t elf::ObjectFile<ELFT>::getMipsGp0() const {
-  if (ELFT::Is64Bits && MipsOptions && MipsOptions->Reginfo)
-    return MipsOptions->Reginfo->ri_gp_value;
-  if (!ELFT::Is64Bits && MipsReginfo && MipsReginfo->Reginfo)
-    return MipsReginfo->Reginfo->ri_gp_value;
-  return 0;
-}
-
 template <class ELFT>
-void elf::ObjectFile<ELFT>::parse(DenseSet<StringRef> &ComdatGroups) {
+void elf::ObjectFile<ELFT>::parse(DenseSet<CachedHashStringRef> &ComdatGroups) {
   // Read section and symbol tables.
   initializeSections(ComdatGroups);
   initializeSymbols();
@@ -137,22 +173,25 @@ void elf::ObjectFile<ELFT>::parse(DenseSet<StringRef> &ComdatGroups) {
 // They are identified and deduplicated by group name. This function
 // returns a group name.
 template <class ELFT>
-StringRef elf::ObjectFile<ELFT>::getShtGroupSignature(const Elf_Shdr &Sec) {
-  const ELFFile<ELFT> &Obj = this->ELFObj;
-  const Elf_Shdr *Symtab = check(Obj.getSection(Sec.sh_link));
-  const Elf_Sym *Sym = Obj.getSymbol(Symtab, Sec.sh_info);
-  StringRef Strtab = check(Obj.getStringTableForSymtab(*Symtab));
-  return check(Sym->getName(Strtab));
+StringRef
+elf::ObjectFile<ELFT>::getShtGroupSignature(ArrayRef<Elf_Shdr> Sections,
+                                            const Elf_Shdr &Sec) {
+  if (this->Symbols.empty())
+    this->initSymtab(Sections,
+                     check(object::getSection<ELFT>(Sections, Sec.sh_link)));
+  const Elf_Sym *Sym =
+      check(object::getSymbol<ELFT>(this->Symbols, Sec.sh_info));
+  return check(Sym->getName(this->StringTable));
 }
 
 template <class ELFT>
 ArrayRef<typename elf::ObjectFile<ELFT>::Elf_Word>
 elf::ObjectFile<ELFT>::getShtGroupEntries(const Elf_Shdr &Sec) {
-  const ELFFile<ELFT> &Obj = this->ELFObj;
+  const ELFFile<ELFT> &Obj = this->getObj();
   ArrayRef<Elf_Word> Entries =
       check(Obj.template getSectionContentsAsArray<Elf_Word>(&Sec));
   if (Entries.empty() || Entries[0] != GRP_COMDAT)
-    fatal(getFilename(this) + ": unsupported SHT_GROUP format");
+    fatal(toString(this) + ": unsupported SHT_GROUP format");
   return Entries.slice(1);
 }
 
@@ -163,15 +202,39 @@ bool elf::ObjectFile<ELFT>::shouldMerge(const Elf_Shdr &Sec) {
   if (Config->Optimize == 0)
     return false;
 
+  // Do not merge sections if generating a relocatable object. It makes
+  // the code simpler because we do not need to update relocation addends
+  // to reflect changes introduced by merging. Instead of that we write
+  // such "merge" sections into separate OutputSections and keep SHF_MERGE
+  // / SHF_STRINGS flags and sh_entsize value to be able to perform merging
+  // later during a final linking.
+  if (Config->Relocatable)
+    return false;
+
+  // A mergeable section with size 0 is useless because they don't have
+  // any data to merge. A mergeable string section with size 0 can be
+  // argued as invalid because it doesn't end with a null character.
+  // We'll avoid a mess by handling them as if they were non-mergeable.
+  if (Sec.sh_size == 0)
+    return false;
+
+  // Check for sh_entsize. The ELF spec is not clear about the zero
+  // sh_entsize. It says that "the member [sh_entsize] contains 0 if
+  // the section does not hold a table of fixed-size entries". We know
+  // that Rust 1.13 produces a string mergeable section with a zero
+  // sh_entsize. Here we just accept it rather than being picky about it.
+  uintX_t EntSize = Sec.sh_entsize;
+  if (EntSize == 0)
+    return false;
+  if (Sec.sh_size % EntSize)
+    fatal(toString(this) +
+          ": SHF_MERGE section size must be a multiple of sh_entsize");
+
   uintX_t Flags = Sec.sh_flags;
   if (!(Flags & SHF_MERGE))
     return false;
   if (Flags & SHF_WRITE)
-    fatal(getFilename(this) + ": writable SHF_MERGE section is not supported");
-  uintX_t EntSize = Sec.sh_entsize;
-  if (!EntSize || Sec.sh_size % EntSize)
-    fatal(getFilename(this) +
-          ": SHF_MERGE section size must be a multiple of sh_entsize");
+    fatal(toString(this) + ": writable SHF_MERGE section is not supported");
 
   // Don't try to merge if the alignment is larger than the sh_entsize and this
   // is not SHF_STRINGS.
@@ -187,74 +250,61 @@ bool elf::ObjectFile<ELFT>::shouldMerge(const Elf_Shdr &Sec) {
 
 template <class ELFT>
 void elf::ObjectFile<ELFT>::initializeSections(
-    DenseSet<StringRef> &ComdatGroups) {
-  uint64_t Size = this->ELFObj.getNumSections();
+    DenseSet<CachedHashStringRef> &ComdatGroups) {
+  ArrayRef<Elf_Shdr> ObjSections = check(this->getObj().sections());
+  const ELFFile<ELFT> &Obj = this->getObj();
+  uint64_t Size = ObjSections.size();
   Sections.resize(Size);
   unsigned I = -1;
-  const ELFFile<ELFT> &Obj = this->ELFObj;
-  for (const Elf_Shdr &Sec : Obj.sections()) {
+  StringRef SectionStringTable = check(Obj.getSectionStringTable(ObjSections));
+  for (const Elf_Shdr &Sec : ObjSections) {
     ++I;
     if (Sections[I] == &InputSection<ELFT>::Discarded)
       continue;
 
+    // SHF_EXCLUDE'ed sections are discarded by the linker. However,
+    // if -r is given, we'll let the final link discard such sections.
+    // This is compatible with GNU.
+    if ((Sec.sh_flags & SHF_EXCLUDE) && !Config->Relocatable) {
+      Sections[I] = &InputSection<ELFT>::Discarded;
+      continue;
+    }
+
     switch (Sec.sh_type) {
     case SHT_GROUP:
       Sections[I] = &InputSection<ELFT>::Discarded;
-      if (ComdatGroups.insert(getShtGroupSignature(Sec)).second)
+      if (ComdatGroups.insert(CachedHashStringRef(
+                                  getShtGroupSignature(ObjSections, Sec)))
+              .second)
         continue;
       for (uint32_t SecIndex : getShtGroupEntries(Sec)) {
         if (SecIndex >= Size)
-          fatal(getFilename(this) + ": invalid section index in group: " +
+          fatal(toString(this) + ": invalid section index in group: " +
                 Twine(SecIndex));
         Sections[SecIndex] = &InputSection<ELFT>::Discarded;
       }
       break;
     case SHT_SYMTAB:
-      this->Symtab = &Sec;
+      this->initSymtab(ObjSections, &Sec);
       break;
     case SHT_SYMTAB_SHNDX:
-      this->SymtabSHNDX = check(Obj.getSHNDXTable(Sec));
+      this->SymtabSHNDX = check(Obj.getSHNDXTable(Sec, ObjSections));
       break;
     case SHT_STRTAB:
     case SHT_NULL:
       break;
-    case SHT_RELA:
-    case SHT_REL: {
-      // This section contains relocation information.
-      // If -r is given, we do not interpret or apply relocation
-      // but just copy relocation sections to output.
-      if (Config->Relocatable) {
-        Sections[I] = new (IAlloc.Allocate()) InputSection<ELFT>(this, &Sec);
-        break;
-      }
-
-      // Find the relocation target section and associate this
-      // section with it.
-      InputSectionBase<ELFT> *Target = getRelocTarget(Sec);
-      if (!Target)
-        break;
-      if (auto *S = dyn_cast<InputSection<ELFT>>(Target)) {
-        S->RelocSections.push_back(&Sec);
-        break;
-      }
-      if (auto *S = dyn_cast<EhInputSection<ELFT>>(Target)) {
-        if (S->RelocSection)
-          fatal(
-              getFilename(this) +
-              ": multiple relocation sections to .eh_frame are not supported");
-        S->RelocSection = &Sec;
-        break;
-      }
-      fatal(getFilename(this) +
-            ": relocations pointing to SHF_MERGE are not supported");
-    }
-    case SHT_ARM_ATTRIBUTES:
-      // FIXME: ARM meta-data section. At present attributes are ignored,
-      // they can be used to reason about object compatibility.
-      Sections[I] = &InputSection<ELFT>::Discarded;
-      break;
     default:
-      Sections[I] = createInputSection(Sec);
+      Sections[I] = createInputSection(Sec, SectionStringTable);
+    }
+
+    // .ARM.exidx sections have a reverse dependency on the InputSection they
+    // have a SHF_LINK_ORDER dependency, this is identified by the sh_link.
+    if (Sec.sh_flags & SHF_LINK_ORDER) {
+      if (Sec.sh_link >= Sections.size())
+        fatal(toString(this) + ": invalid sh_link index: " +
+              Twine(Sec.sh_link));
+      auto *IS = cast<InputSection<ELFT>>(Sections[Sec.sh_link]);
+      IS->DependentSection = Sections[I];
     }
   }
 }
@@ -264,8 +314,7 @@ InputSectionBase<ELFT> *
 elf::ObjectFile<ELFT>::getRelocTarget(const Elf_Shdr &Sec) {
   uint32_t Idx = Sec.sh_info;
   if (Idx >= Sections.size())
-    fatal(getFilename(this) + ": invalid relocated section index: " +
-          Twine(Idx));
+    fatal(toString(this) + ": invalid relocated section index: " + Twine(Idx));
   InputSectionBase<ELFT> *Target = Sections[Idx];
 
   // Strictly speaking, a relocation section must be included in the
@@ -275,14 +324,65 @@ elf::ObjectFile<ELFT>::getRelocTarget(const Elf_Shdr &Sec) {
     return nullptr;
 
   if (!Target)
-    fatal(getFilename(this) + ": unsupported relocation reference");
+    fatal(toString(this) + ": unsupported relocation reference");
   return Target;
 }
 
 template <class ELFT>
 InputSectionBase<ELFT> *
-elf::ObjectFile<ELFT>::createInputSection(const Elf_Shdr &Sec) {
-  StringRef Name = check(this->ELFObj.getSectionName(&Sec));
+elf::ObjectFile<ELFT>::createInputSection(const Elf_Shdr &Sec,
+                                          StringRef SectionStringTable) {
+  StringRef Name =
+      check(this->getObj().getSectionName(&Sec, SectionStringTable));
+
+  switch (Sec.sh_type) {
+  case SHT_ARM_ATTRIBUTES:
+    // FIXME: ARM meta-data section. Retain the first attribute section
+    // we see. The eglibc ARM dynamic loaders require the presence of an
+    // attribute section for dlopen to work.
+    // In a full implementation we would merge all attribute sections.
+    if (In<ELFT>::ARMAttributes == nullptr) {
+      In<ELFT>::ARMAttributes = make<InputSection<ELFT>>(this, &Sec, Name);
+      return In<ELFT>::ARMAttributes;
+    }
+    return &InputSection<ELFT>::Discarded;
+  case SHT_RELA:
+  case SHT_REL: {
+    // This section contains relocation information.
+    // If -r is given, we do not interpret or apply relocation
+    // but just copy relocation sections to output.
+    if (Config->Relocatable)
+      return make<InputSection<ELFT>>(this, &Sec, Name);
+
+    // Find the relocation target section and associate this
+    // section with it.
+    InputSectionBase<ELFT> *Target = getRelocTarget(Sec);
+    if (!Target)
+      return nullptr;
+    if (Target->FirstRelocation)
+      fatal(toString(this) +
+            ": multiple relocation sections to one section are not supported");
+    if (!isa<InputSection<ELFT>>(Target) && !isa<EhInputSection<ELFT>>(Target))
+      fatal(toString(this) +
+            ": relocations pointing to SHF_MERGE are not supported");
+
+    size_t NumRelocations;
+    if (Sec.sh_type == SHT_RELA) {
+      ArrayRef<Elf_Rela> Rels = check(this->getObj().relas(&Sec));
+      Target->FirstRelocation = Rels.begin();
+      NumRelocations = Rels.size();
+      Target->AreRelocsRela = true;
+    } else {
+      ArrayRef<Elf_Rel> Rels = check(this->getObj().rels(&Sec));
+      Target->FirstRelocation = Rels.begin();
+      NumRelocations = Rels.size();
+      Target->AreRelocsRela = false;
+    }
+    assert(isUInt<31>(NumRelocations));
+    Target->NumRelocations = NumRelocations;
+    return nullptr;
+  }
+  }
 
   // .note.GNU-stack is a marker section to control the presence of
   // PT_GNU_STACK segment in outputs. Since the presence of the segment
@@ -296,39 +396,23 @@ elf::ObjectFile<ELFT>::createInputSection(const Elf_Shdr &Sec) {
     return &InputSection<ELFT>::Discarded;
   }
 
-  if (Config->StripDebug && Name.startswith(".debug"))
+  if (Config->Strip != StripPolicy::None && Name.startswith(".debug"))
     return &InputSection<ELFT>::Discarded;
 
-  // A MIPS object file has a special sections that contain register
-  // usage info, which need to be handled by the linker specially.
-  if (Config->EMachine == EM_MIPS) {
-    if (Name == ".reginfo") {
-      MipsReginfo.reset(new MipsReginfoInputSection<ELFT>(this, &Sec));
-      return MipsReginfo.get();
-    }
-    if (Name == ".MIPS.options") {
-      MipsOptions.reset(new MipsOptionsInputSection<ELFT>(this, &Sec));
-      return MipsOptions.get();
-    }
-  }
-
   // The linker merges EH (exception handling) frames and creates a
   // .eh_frame_hdr section for runtime. So we handle them with a special
   // class. For relocatable outputs, they are just passed through.
   if (Name == ".eh_frame" && !Config->Relocatable)
-    return new (EHAlloc.Allocate()) EhInputSection<ELFT>(this, &Sec);
+    return make<EhInputSection<ELFT>>(this, &Sec, Name);
 
   if (shouldMerge(Sec))
-    return new (MAlloc.Allocate()) MergeInputSection<ELFT>(this, &Sec);
-  return new (IAlloc.Allocate()) InputSection<ELFT>(this, &Sec);
+    return make<MergeInputSection<ELFT>>(this, &Sec, Name);
+  return make<InputSection<ELFT>>(this, &Sec, Name);
 }
 
 template <class ELFT> void elf::ObjectFile<ELFT>::initializeSymbols() {
-  this->initStringTable();
-  Elf_Sym_Range Syms = this->getElfSymbols(false);
-  uint32_t NumSymbols = std::distance(Syms.begin(), Syms.end());
-  SymbolBodies.reserve(NumSymbols);
-  for (const Elf_Sym &Sym : Syms)
+  SymbolBodies.reserve(this->Symbols.size());
+  for (const Elf_Sym &Sym : this->Symbols)
     SymbolBodies.push_back(createSymbolBody(&Sym));
 }
 
@@ -336,12 +420,23 @@ template <class ELFT>
 InputSectionBase<ELFT> *
 elf::ObjectFile<ELFT>::getSection(const Elf_Sym &Sym) const {
   uint32_t Index = this->getSectionIndex(Sym);
-  if (Index == 0)
-    return nullptr;
-  if (Index >= Sections.size() || !Sections[Index])
-    fatal(getFilename(this) + ": invalid section index: " + Twine(Index));
+  if (Index >= Sections.size())
+    fatal(toString(this) + ": invalid section index: " + Twine(Index));
   InputSectionBase<ELFT> *S = Sections[Index];
-  if (S == &InputSectionBase<ELFT>::Discarded)
+
+  // We found that GNU assembler 2.17.50 [FreeBSD] 2007-07-03 could
+  // generate broken objects. STT_SECTION/STT_NOTYPE symbols can be
+  // associated with SHT_REL[A]/SHT_SYMTAB/SHT_STRTAB sections.
+  // In this case it is fine for section to be null here as we do not
+  // allocate sections of these types.
+  if (!S) {
+    if (Index == 0 || Sym.getType() == STT_SECTION ||
+        Sym.getType() == STT_NOTYPE)
+      return nullptr;
+    fatal(toString(this) + ": invalid section index: " + Twine(Index));
+  }
+
+  if (S == &InputSection<ELFT>::Discarded)
     return S;
   return S->Repl;
 }
@@ -350,11 +445,26 @@ template <class ELFT>
 SymbolBody *elf::ObjectFile<ELFT>::createSymbolBody(const Elf_Sym *Sym) {
   int Binding = Sym->getBinding();
   InputSectionBase<ELFT> *Sec = getSection(*Sym);
+
+  uint8_t StOther = Sym->st_other;
+  uint8_t Type = Sym->getType();
+  uintX_t Value = Sym->st_value;
+  uintX_t Size = Sym->st_size;
+
   if (Binding == STB_LOCAL) {
+    if (Sym->getType() == STT_FILE)
+      SourceFile = check(Sym->getName(this->StringTable));
+
+    if (this->StringTable.size() <= Sym->st_name)
+      fatal(toString(this) + ": invalid symbol name offset");
+
+    StringRefZ Name = this->StringTable.data() + Sym->st_name;
     if (Sym->st_shndx == SHN_UNDEF)
-      return new (this->Alloc)
-          Undefined(Sym->st_name, Sym->st_other, Sym->getType(), this);
-    return new (this->Alloc) DefinedRegular<ELFT>(*Sym, Sec);
+      return new (BAlloc)
+          Undefined(Name, /*IsLocal=*/true, StOther, Type, this);
+
+    return new (BAlloc) DefinedRegular<ELFT>(Name, /*IsLocal=*/true, StOther,
+                                             Type, Value, Size, Sec, this);
   }
 
   StringRef Name = check(Sym->getName(this->StringTable));
@@ -362,33 +472,38 @@ SymbolBody *elf::ObjectFile<ELFT>::createSymbolBody(const Elf_Sym *Sym) {
   switch (Sym->st_shndx) {
   case SHN_UNDEF:
     return elf::Symtab<ELFT>::X
-        ->addUndefined(Name, Binding, Sym->st_other, Sym->getType(),
-                       /*CanOmitFromDynSym*/ false, this)
+        ->addUndefined(Name, /*IsLocal=*/false, Binding, StOther, Type,
+                       /*CanOmitFromDynSym=*/false, this)
         ->body();
   case SHN_COMMON:
+    if (Value == 0 || Value >= UINT32_MAX)
+      fatal(toString(this) + ": common symbol '" + Name +
+            "' has invalid alignment: " + Twine(Value));
     return elf::Symtab<ELFT>::X
-        ->addCommon(Name, Sym->st_size, Sym->st_value, Binding, Sym->st_other,
-                    Sym->getType(), this)
+        ->addCommon(Name, Size, Value, Binding, StOther, Type, this)
         ->body();
   }
 
   switch (Binding) {
   default:
-    fatal(getFilename(this) + ": unexpected binding: " + Twine(Binding));
+    fatal(toString(this) + ": unexpected binding: " + Twine(Binding));
   case STB_GLOBAL:
   case STB_WEAK:
   case STB_GNU_UNIQUE:
     if (Sec == &InputSection<ELFT>::Discarded)
       return elf::Symtab<ELFT>::X
-          ->addUndefined(Name, Binding, Sym->st_other, Sym->getType(),
-                         /*CanOmitFromDynSym*/ false, this)
+          ->addUndefined(Name, /*IsLocal=*/false, Binding, StOther, Type,
+                         /*CanOmitFromDynSym=*/false, this)
           ->body();
-    return elf::Symtab<ELFT>::X->addRegular(Name, *Sym, Sec)->body();
+    return elf::Symtab<ELFT>::X
+        ->addRegular(Name, StOther, Type, Value, Size, Binding, Sec, this)
+        ->body();
   }
 }
 
 template <class ELFT> void ArchiveFile::parse() {
-  File = check(Archive::create(MB), "failed to parse archive");
+  File = check(Archive::create(MB),
+               MB.getBufferIdentifier() + ": failed to parse archive");
 
   // Read the symbol table to construct Lazy objects.
   for (const Archive::Symbol &Sym : File->symbols())
@@ -396,13 +511,14 @@ template <class ELFT> void ArchiveFile::parse() {
 }
 
 // Returns a buffer pointing to a member file containing a given symbol.
-MemoryBufferRef ArchiveFile::getMember(const Archive::Symbol *Sym) {
+std::pair<MemoryBufferRef, uint64_t>
+ArchiveFile::getMember(const Archive::Symbol *Sym) {
   Archive::Child C =
       check(Sym->getMember(),
             "could not get the member for symbol " + Sym->getName());
 
   if (!Seen.insert(C.getChildOffset()).second)
-    return MemoryBufferRef();
+    return {MemoryBufferRef(), 0};
 
   MemoryBufferRef Ret =
       check(C.getMemoryBufferRef(),
@@ -412,8 +528,9 @@ MemoryBufferRef ArchiveFile::getMember(const Archive::Symbol *Sym) {
   if (C.getParent()->isThin() && Driver->Cpio)
     Driver->Cpio->append(relativeToRoot(check(C.getFullName())),
                          Ret.getBuffer());
-
-  return Ret;
+  if (C.getParent()->isThin())
+    return {Ret, 0};
+  return {Ret, C.getChildOffset()};
 }
 
 template <class ELFT>
@@ -423,32 +540,29 @@ SharedFile<ELFT>::SharedFile(MemoryBufferRef M)
 template <class ELFT>
 const typename ELFT::Shdr *
 SharedFile<ELFT>::getSection(const Elf_Sym &Sym) const {
-  uint32_t Index = this->getSectionIndex(Sym);
-  if (Index == 0)
-    return nullptr;
-  return check(this->ELFObj.getSection(Index));
+  return check(
+      this->getObj().getSection(&Sym, this->Symbols, this->SymtabSHNDX));
 }
 
 // Partially parse the shared object file so that we can call
 // getSoName on this object.
 template <class ELFT> void SharedFile<ELFT>::parseSoName() {
-  typedef typename ELFT::Dyn Elf_Dyn;
-  typedef typename ELFT::uint uintX_t;
   const Elf_Shdr *DynamicSec = nullptr;
 
-  const ELFFile<ELFT> Obj = this->ELFObj;
-  for (const Elf_Shdr &Sec : Obj.sections()) {
+  const ELFFile<ELFT> Obj = this->getObj();
+  ArrayRef<Elf_Shdr> Sections = check(Obj.sections());
+  for (const Elf_Shdr &Sec : Sections) {
     switch (Sec.sh_type) {
     default:
       continue;
     case SHT_DYNSYM:
-      this->Symtab = &Sec;
+      this->initSymtab(Sections, &Sec);
       break;
     case SHT_DYNAMIC:
       DynamicSec = &Sec;
       break;
     case SHT_SYMTAB_SHNDX:
-      this->SymtabSHNDX = check(Obj.getSHNDXTable(Sec));
+      this->SymtabSHNDX = check(Obj.getSHNDXTable(Sec, Sections));
       break;
     case SHT_GNU_versym:
       this->VersymSec = &Sec;
@@ -459,20 +573,25 @@ template <class ELFT> void SharedFile<ELFT>::parseSoName() {
     }
   }
 
-  this->initStringTable();
+  if (this->VersymSec && this->Symbols.empty())
+    error("SHT_GNU_versym should be associated with symbol table");
+
+  // DSOs are identified by soname, and they usually contain
+  // DT_SONAME tag in their header. But if they are missing,
+  // filenames are used as default sonames.
   SoName = sys::path::filename(this->getName());
 
   if (!DynamicSec)
     return;
-  auto *Begin =
-      reinterpret_cast<const Elf_Dyn *>(Obj.base() + DynamicSec->sh_offset);
-  const Elf_Dyn *End = Begin + DynamicSec->sh_size / sizeof(Elf_Dyn);
 
-  for (const Elf_Dyn &Dyn : make_range(Begin, End)) {
+  ArrayRef<Elf_Dyn> Arr =
+      check(Obj.template getSectionContentsAsArray<Elf_Dyn>(DynamicSec),
+            toString(this) + ": getSectionContentsAsArray failed");
+  for (const Elf_Dyn &Dyn : Arr) {
     if (Dyn.d_tag == DT_SONAME) {
       uintX_t Val = Dyn.getVal();
       if (Val >= this->StringTable.size())
-        fatal(getFilename(this) + ": invalid DT_SONAME entry");
+        fatal(toString(this) + ": invalid DT_SONAME entry");
       SoName = StringRef(this->StringTable.data() + Val);
       return;
     }
@@ -494,9 +613,9 @@ SharedFile<ELFT>::parseVerdefs(const Elf_Versym *&Versym) {
     return Verdefs;
 
   // The location of the first global versym entry.
-  Versym = reinterpret_cast<const Elf_Versym *>(this->ELFObj.base() +
-                                                VersymSec->sh_offset) +
-           this->Symtab->sh_info;
+  const char *Base = this->MB.getBuffer().data();
+  Versym = reinterpret_cast<const Elf_Versym *>(Base + VersymSec->sh_offset) +
+           this->FirstNonLocal;
 
   // We cannot determine the largest verdef identifier without inspecting
   // every Elf_Verdef, but both bfd and gold assign verdef identifiers
@@ -507,7 +626,7 @@ SharedFile<ELFT>::parseVerdefs(const Elf_Versym *&Versym) {
 
   // Build the Verdefs array by following the chain of Elf_Verdef objects
   // from the start of the .gnu.version_d section.
-  const uint8_t *Verdef = this->ELFObj.base() + VerdefSec->sh_offset;
+  const char *Verdef = Base + VerdefSec->sh_offset;
   for (unsigned I = 0; I != VerdefCount; ++I) {
     auto *CurVerdef = reinterpret_cast<const Elf_Verdef *>(Verdef);
     Verdef += CurVerdef->vd_next;
@@ -526,7 +645,7 @@ template <class ELFT> void SharedFile<ELFT>::parseRest() {
   const Elf_Versym *Versym = nullptr;
   std::vector<const Elf_Verdef *> Verdefs = parseVerdefs(Versym);
 
-  Elf_Sym_Range Syms = this->getElfSymbols(true);
+  Elf_Sym_Range Syms = this->getGlobalSymbols();
   for (const Elf_Sym &Sym : Syms) {
     unsigned VersymIndex = 0;
     if (Versym) {
@@ -552,18 +671,16 @@ template <class ELFT> void SharedFile<ELFT>::parseRest() {
   }
 }
 
-static ELFKind getELFKind(MemoryBufferRef MB) {
-  std::string TripleStr = getBitcodeTargetTriple(MB, Driver->Context);
-  Triple TheTriple(TripleStr);
-  bool Is64Bits = TheTriple.isArch64Bit();
-  if (TheTriple.isLittleEndian())
-    return Is64Bits ? ELF64LEKind : ELF32LEKind;
-  return Is64Bits ? ELF64BEKind : ELF32BEKind;
+static ELFKind getBitcodeELFKind(MemoryBufferRef MB) {
+  Triple T(check(getBitcodeTargetTriple(MB)));
+  if (T.isLittleEndian())
+    return T.isArch64Bit() ? ELF64LEKind : ELF32LEKind;
+  return T.isArch64Bit() ? ELF64BEKind : ELF32BEKind;
 }
 
-static uint8_t getMachineKind(MemoryBufferRef MB) {
-  std::string TripleStr = getBitcodeTargetTriple(MB, Driver->Context);
-  switch (Triple(TripleStr).getArch()) {
+static uint8_t getBitcodeMachineKind(MemoryBufferRef MB) {
+  Triple T(check(getBitcodeTargetTriple(MB)));
+  switch (T.getArch()) {
   case Triple::aarch64:
     return EM_AARCH64;
   case Triple::arm:
@@ -578,23 +695,22 @@ static uint8_t getMachineKind(MemoryBufferRef MB) {
   case Triple::ppc64:
     return EM_PPC64;
   case Triple::x86:
-    return EM_386;
+    return T.isOSIAMCU() ? EM_IAMCU : EM_386;
   case Triple::x86_64:
     return EM_X86_64;
   default:
     fatal(MB.getBufferIdentifier() +
-          ": could not infer e_machine from bitcode target triple " +
-          TripleStr);
+          ": could not infer e_machine from bitcode target triple " + T.str());
   }
 }
 
 BitcodeFile::BitcodeFile(MemoryBufferRef MB) : InputFile(BitcodeKind, MB) {
-  EKind = getELFKind(MB);
-  EMachine = getMachineKind(MB);
+  EKind = getBitcodeELFKind(MB);
+  EMachine = getBitcodeMachineKind(MB);
 }
 
-static uint8_t getGvVisibility(const GlobalValue *GV) {
-  switch (GV->getVisibility()) {
+static uint8_t mapVisibility(GlobalValue::VisibilityTypes GvVisibility) {
+  switch (GvVisibility) {
   case GlobalValue::DefaultVisibility:
     return STV_DEFAULT;
   case GlobalValue::HiddenVisibility:
@@ -606,124 +722,134 @@ static uint8_t getGvVisibility(const GlobalValue *GV) {
 }
 
 template <class ELFT>
-Symbol *BitcodeFile::createSymbol(const DenseSet<const Comdat *> &KeptComdats,
-                                  const IRObjectFile &Obj,
-                                  const BasicSymbolRef &Sym) {
-  const GlobalValue *GV = Obj.getSymbolGV(Sym.getRawDataRefImpl());
-
-  SmallString<64> Name;
-  raw_svector_ostream OS(Name);
-  Sym.printName(OS);
-  StringRef NameRef = Saver.save(StringRef(Name));
-
-  uint32_t Flags = Sym.getFlags();
-  bool IsWeak = Flags & BasicSymbolRef::SF_Weak;
-  uint32_t Binding = IsWeak ? STB_WEAK : STB_GLOBAL;
-
-  uint8_t Type = STT_NOTYPE;
-  bool CanOmitFromDynSym = false;
-  // FIXME: Expose a thread-local flag for module asm symbols.
-  if (GV) {
-    if (GV->isThreadLocal())
-      Type = STT_TLS;
-    CanOmitFromDynSym = canBeOmittedFromSymbolTable(GV);
-  }
-
-  uint8_t Visibility;
-  if (GV)
-    Visibility = getGvVisibility(GV);
-  else
-    // FIXME: Set SF_Hidden flag correctly for module asm symbols, and expose
-    // protected visibility.
-    Visibility = STV_DEFAULT;
-
-  if (GV)
-    if (const Comdat *C = GV->getComdat())
-      if (!KeptComdats.count(C))
-        return Symtab<ELFT>::X->addUndefined(NameRef, Binding, Visibility, Type,
-                                             CanOmitFromDynSym, this);
+static Symbol *createBitcodeSymbol(const std::vector<bool> &KeptComdats,
+                                   const lto::InputFile::Symbol &ObjSym,
+                                   BitcodeFile *F) {
+  StringRef NameRef = Saver.save(ObjSym.getName());
+  uint32_t Flags = ObjSym.getFlags();
+  uint32_t Binding = (Flags & BasicSymbolRef::SF_Weak) ? STB_WEAK : STB_GLOBAL;
+
+  uint8_t Type = ObjSym.isTLS() ? STT_TLS : STT_NOTYPE;
+  uint8_t Visibility = mapVisibility(ObjSym.getVisibility());
+  bool CanOmitFromDynSym = ObjSym.canBeOmittedFromSymbolTable();
+
+  int C = check(ObjSym.getComdatIndex());
+  if (C != -1 && !KeptComdats[C])
+    return Symtab<ELFT>::X->addUndefined(NameRef, /*IsLocal=*/false, Binding,
+                                         Visibility, Type, CanOmitFromDynSym,
+                                         F);
 
-  const Module &M = Obj.getModule();
   if (Flags & BasicSymbolRef::SF_Undefined)
-    return Symtab<ELFT>::X->addUndefined(NameRef, Binding, Visibility, Type,
-                                         CanOmitFromDynSym, this);
-  if (Flags & BasicSymbolRef::SF_Common) {
-    // FIXME: Set SF_Common flag correctly for module asm symbols, and expose
-    // size and alignment.
-    assert(GV);
-    const DataLayout &DL = M.getDataLayout();
-    uint64_t Size = DL.getTypeAllocSize(GV->getValueType());
-    return Symtab<ELFT>::X->addCommon(NameRef, Size, GV->getAlignment(),
-                                      Binding, Visibility, STT_OBJECT, this);
-  }
-  return Symtab<ELFT>::X->addBitcode(NameRef, IsWeak, Visibility, Type,
-                                     CanOmitFromDynSym, this);
-}
+    return Symtab<ELFT>::X->addUndefined(NameRef, /*IsLocal=*/false, Binding,
+                                         Visibility, Type, CanOmitFromDynSym,
+                                         F);
+
+  if (Flags & BasicSymbolRef::SF_Common)
+    return Symtab<ELFT>::X->addCommon(NameRef, ObjSym.getCommonSize(),
+                                      ObjSym.getCommonAlignment(), Binding,
+                                      Visibility, STT_OBJECT, F);
 
-bool BitcodeFile::shouldSkip(uint32_t Flags) {
-  return !(Flags & BasicSymbolRef::SF_Global) ||
-         (Flags & BasicSymbolRef::SF_FormatSpecific);
+  return Symtab<ELFT>::X->addBitcode(NameRef, Binding, Visibility, Type,
+                                     CanOmitFromDynSym, F);
 }
 
 template <class ELFT>
-void BitcodeFile::parse(DenseSet<StringRef> &ComdatGroups) {
-  Obj = check(IRObjectFile::create(MB, Driver->Context));
-  const Module &M = Obj->getModule();
-
-  DenseSet<const Comdat *> KeptComdats;
-  for (const auto &P : M.getComdatSymbolTable()) {
-    StringRef N = Saver.save(P.first());
-    if (ComdatGroups.insert(N).second)
-      KeptComdats.insert(&P.second);
+void BitcodeFile::parse(DenseSet<CachedHashStringRef> &ComdatGroups) {
+
+  // Here we pass a new MemoryBufferRef which is identified by ArchiveName
+  // (the fully resolved path of the archive) + member name + offset of the
+  // member in the archive.
+  // ThinLTO uses the MemoryBufferRef identifier to access its internal
+  // data structures and if two archives define two members with the same name,
+  // this causes a collision which result in only one of the objects being
+  // taken into consideration at LTO time (which very likely causes undefined
+  // symbols later in the link stage).
+  Obj = check(lto::InputFile::create(MemoryBufferRef(
+      MB.getBuffer(), Saver.save(ArchiveName + MB.getBufferIdentifier() +
+                                 utostr(OffsetInArchive)))));
+
+  std::vector<bool> KeptComdats;
+  for (StringRef S : Obj->getComdatTable()) {
+    StringRef N = Saver.save(S);
+    KeptComdats.push_back(ComdatGroups.insert(CachedHashStringRef(N)).second);
   }
 
-  for (const BasicSymbolRef &Sym : Obj->symbols())
-    if (!shouldSkip(Sym.getFlags()))
-      Symbols.push_back(createSymbol<ELFT>(KeptComdats, *Obj, Sym));
+  for (const lto::InputFile::Symbol &ObjSym : Obj->symbols())
+    Symbols.push_back(createBitcodeSymbol<ELFT>(KeptComdats, ObjSym, this));
 }
 
 template <template <class> class T>
-static std::unique_ptr<InputFile> createELFFile(MemoryBufferRef MB) {
+static InputFile *createELFFile(MemoryBufferRef MB) {
   unsigned char Size;
   unsigned char Endian;
   std::tie(Size, Endian) = getElfArchType(MB.getBuffer());
   if (Endian != ELFDATA2LSB && Endian != ELFDATA2MSB)
-    fatal("invalid data encoding: " + MB.getBufferIdentifier());
+    fatal(MB.getBufferIdentifier() + ": invalid data encoding");
+
+  size_t BufSize = MB.getBuffer().size();
+  if ((Size == ELFCLASS32 && BufSize < sizeof(Elf32_Ehdr)) ||
+      (Size == ELFCLASS64 && BufSize < sizeof(Elf64_Ehdr)))
+    fatal(MB.getBufferIdentifier() + ": file is too short");
 
-  std::unique_ptr<InputFile> Obj;
+  InputFile *Obj;
   if (Size == ELFCLASS32 && Endian == ELFDATA2LSB)
-    Obj.reset(new T<ELF32LE>(MB));
+    Obj = make<T<ELF32LE>>(MB);
   else if (Size == ELFCLASS32 && Endian == ELFDATA2MSB)
-    Obj.reset(new T<ELF32BE>(MB));
+    Obj = make<T<ELF32BE>>(MB);
   else if (Size == ELFCLASS64 && Endian == ELFDATA2LSB)
-    Obj.reset(new T<ELF64LE>(MB));
+    Obj = make<T<ELF64LE>>(MB);
   else if (Size == ELFCLASS64 && Endian == ELFDATA2MSB)
-    Obj.reset(new T<ELF64BE>(MB));
+    Obj = make<T<ELF64BE>>(MB);
   else
-    fatal("invalid file class: " + MB.getBufferIdentifier());
+    fatal(MB.getBufferIdentifier() + ": invalid file class");
 
   if (!Config->FirstElf)
-    Config->FirstElf = Obj.get();
+    Config->FirstElf = Obj;
   return Obj;
 }
 
+template <class ELFT> void BinaryFile::parse() {
+  StringRef Buf = MB.getBuffer();
+  ArrayRef<uint8_t> Data =
+      makeArrayRef<uint8_t>((const uint8_t *)Buf.data(), Buf.size());
+
+  std::string Filename = MB.getBufferIdentifier();
+  std::transform(Filename.begin(), Filename.end(), Filename.begin(),
+                 [](char C) { return isalnum(C) ? C : '_'; });
+  Filename = "_binary_" + Filename;
+  StringRef StartName = Saver.save(Twine(Filename) + "_start");
+  StringRef EndName = Saver.save(Twine(Filename) + "_end");
+  StringRef SizeName = Saver.save(Twine(Filename) + "_size");
+
+  auto *Section =
+      make<InputSection<ELFT>>(SHF_ALLOC, SHT_PROGBITS, 8, Data, ".data");
+  Sections.push_back(Section);
+
+  elf::Symtab<ELFT>::X->addRegular(StartName, STV_DEFAULT, STT_OBJECT, 0, 0,
+                                   STB_GLOBAL, Section, nullptr);
+  elf::Symtab<ELFT>::X->addRegular(EndName, STV_DEFAULT, STT_OBJECT,
+                                   Data.size(), 0, STB_GLOBAL, Section,
+                                   nullptr);
+  elf::Symtab<ELFT>::X->addRegular(SizeName, STV_DEFAULT, STT_OBJECT,
+                                   Data.size(), 0, STB_GLOBAL, nullptr,
+                                   nullptr);
+}
+
 static bool isBitcode(MemoryBufferRef MB) {
   using namespace sys::fs;
   return identify_magic(MB.getBuffer()) == file_magic::bitcode;
 }
 
-std::unique_ptr<InputFile> elf::createObjectFile(MemoryBufferRef MB,
-                                                 StringRef ArchiveName) {
-  std::unique_ptr<InputFile> F;
-  if (isBitcode(MB))
-    F.reset(new BitcodeFile(MB));
-  else
-    F = createELFFile<ObjectFile>(MB);
+InputFile *elf::createObjectFile(MemoryBufferRef MB, StringRef ArchiveName,
+                                 uint64_t OffsetInArchive) {
+  InputFile *F =
+      isBitcode(MB) ? make<BitcodeFile>(MB) : createELFFile<ObjectFile>(MB);
   F->ArchiveName = ArchiveName;
+  F->OffsetInArchive = OffsetInArchive;
   return F;
 }
 
-std::unique_ptr<InputFile> elf::createSharedFile(MemoryBufferRef MB) {
+InputFile *elf::createSharedFile(MemoryBufferRef MB) {
   return createELFFile<SharedFile>(MB);
 }
 
@@ -734,8 +860,7 @@ MemoryBufferRef LazyObjectFile::getBuffer() {
   return MB;
 }
 
-template <class ELFT>
-void LazyObjectFile::parse() {
+template <class ELFT> void LazyObjectFile::parse() {
   for (StringRef Sym : getSymbols())
     Symtab<ELFT>::X->addLazyObject(Sym, *this);
 }
@@ -745,13 +870,14 @@ template <class ELFT> std::vector<StringRef> LazyObjectFile::getElfSymbols() {
   typedef typename ELFT::Sym Elf_Sym;
   typedef typename ELFT::SymRange Elf_Sym_Range;
 
-  const ELFFile<ELFT> Obj = createELFObj<ELFT>(this->MB);
-  for (const Elf_Shdr &Sec : Obj.sections()) {
+  const ELFFile<ELFT> Obj(this->MB.getBuffer());
+  ArrayRef<Elf_Shdr> Sections = check(Obj.sections());
+  for (const Elf_Shdr &Sec : Sections) {
     if (Sec.sh_type != SHT_SYMTAB)
       continue;
-    Elf_Sym_Range Syms = Obj.symbols(&Sec);
+    Elf_Sym_Range Syms = check(Obj.symbols(&Sec));
     uint32_t FirstNonLocal = Sec.sh_info;
-    StringRef StringTable = check(Obj.getStringTableForSymtab(Sec));
+    StringRef StringTable = check(Obj.getStringTableForSymtab(Sec, Sections));
     std::vector<StringRef> V;
     for (const Elf_Sym &Sym : Syms.slice(FirstNonLocal))
       if (Sym.st_shndx != SHN_UNDEF)
@@ -762,21 +888,11 @@ template <class ELFT> std::vector<StringRef> LazyObjectFile::getElfSymbols() {
 }
 
 std::vector<StringRef> LazyObjectFile::getBitcodeSymbols() {
-  LLVMContext Context;
-  std::unique_ptr<IRObjectFile> Obj =
-      check(IRObjectFile::create(this->MB, Context));
+  std::unique_ptr<lto::InputFile> Obj = check(lto::InputFile::create(this->MB));
   std::vector<StringRef> V;
-  for (const BasicSymbolRef &Sym : Obj->symbols()) {
-    uint32_t Flags = Sym.getFlags();
-    if (BitcodeFile::shouldSkip(Flags))
-      continue;
-    if (Flags & BasicSymbolRef::SF_Undefined)
-      continue;
-    SmallString<64> Name;
-    raw_svector_ostream OS(Name);
-    Sym.printName(OS);
-    V.push_back(Saver.save(StringRef(Name)));
-  }
+  for (const lto::InputFile::Symbol &Sym : Obj->symbols())
+    if (!(Sym.getFlags() & BasicSymbolRef::SF_Undefined))
+      V.push_back(Saver.save(Sym.getName()));
   return V;
 }
 
@@ -803,10 +919,10 @@ template void ArchiveFile::parse<ELF32BE>();
 template void ArchiveFile::parse<ELF64LE>();
 template void ArchiveFile::parse<ELF64BE>();
 
-template void BitcodeFile::parse<ELF32LE>(DenseSet<StringRef> &);
-template void BitcodeFile::parse<ELF32BE>(DenseSet<StringRef> &);
-template void BitcodeFile::parse<ELF64LE>(DenseSet<StringRef> &);
-template void BitcodeFile::parse<ELF64BE>(DenseSet<StringRef> &);
+template void BitcodeFile::parse<ELF32LE>(DenseSet<CachedHashStringRef> &);
+template void BitcodeFile::parse<ELF32BE>(DenseSet<CachedHashStringRef> &);
+template void BitcodeFile::parse<ELF64LE>(DenseSet<CachedHashStringRef> &);
+template void BitcodeFile::parse<ELF64BE>(DenseSet<CachedHashStringRef> &);
 
 template void LazyObjectFile::parse<ELF32LE>();
 template void LazyObjectFile::parse<ELF32BE>();
@@ -827,3 +943,8 @@ template class elf::SharedFile<ELF32LE>;
 template class elf::SharedFile<ELF32BE>;
 template class elf::SharedFile<ELF64LE>;
 template class elf::SharedFile<ELF64BE>;
+
+template void BinaryFile::parse<ELF32LE>();
+template void BinaryFile::parse<ELF32BE>();
+template void BinaryFile::parse<ELF64LE>();
+template void BinaryFile::parse<ELF64BE>();
diff --git a/ELF/InputFiles.h b/ELF/InputFiles.h
index 79cb751494b3..aba1d71379b0 100644
--- a/ELF/InputFiles.h
+++ b/ELF/InputFiles.h
@@ -16,16 +16,24 @@
 #include "Symbols.h"
 
 #include "lld/Core/LLVM.h"
+#include "lld/Core/Reproduce.h"
+#include "llvm/ADT/CachedHashString.h"
 #include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/IR/Comdat.h"
 #include "llvm/Object/Archive.h"
 #include "llvm/Object/ELF.h"
 #include "llvm/Object/IRObjectFile.h"
-#include "llvm/Support/StringSaver.h"
 
 #include <map>
 
+namespace llvm {
+class DWARFDebugLine;
+namespace lto {
+class InputFile;
+}
+}
+
 namespace lld {
 namespace elf {
 
@@ -44,6 +52,7 @@ public:
     LazyObjectKind,
     ArchiveKind,
     BitcodeKind,
+    BinaryKind,
   };
 
   Kind kind() const { return FileKind; }
@@ -56,10 +65,17 @@ public:
   // string for creating error messages.
   StringRef ArchiveName;
 
+  // If this file is in an archive, the member contains the offset of
+  // the file in the archive. Otherwise, it's just zero. We store this
+  // field so that we can pass it to lib/LTO in order to disambiguate
+  // between objects.
+  uint64_t OffsetInArchive;
+
   // If this is an architecture-specific file, the following members
   // have ELF type (i.e. ELF{32,64}{LE,BE}) and target machine type.
   ELFKind EKind = ELFNoneKind;
   uint16_t EMachine = llvm::ELF::EM_NONE;
+  uint8_t OSABI = 0;
 
 protected:
   InputFile(Kind K, MemoryBufferRef M) : MB(M), FileKind(K) {}
@@ -69,7 +85,7 @@ private:
 };
 
 // Returns "(internal)", "foo.a(bar.o)" or "baz.o".
-std::string getFilename(const InputFile *F);
+std::string toString(const InputFile *F);
 
 template <typename ELFT> class ELFFileBase : public InputFile {
 public:
@@ -84,37 +100,37 @@ public:
     return K == ObjectKind || K == SharedKind;
   }
 
-  const llvm::object::ELFFile<ELFT> &getObj() const { return ELFObj; }
-  llvm::object::ELFFile<ELFT> &getObj() { return ELFObj; }
-
-  uint8_t getOSABI() const {
-    return getObj().getHeader()->e_ident[llvm::ELF::EI_OSABI];
+  llvm::object::ELFFile<ELFT> getObj() const {
+    return llvm::object::ELFFile<ELFT>(MB.getBuffer());
   }
 
   StringRef getStringTable() const { return StringTable; }
 
   uint32_t getSectionIndex(const Elf_Sym &Sym) const;
 
-  Elf_Sym_Range getElfSymbols(bool OnlyGlobals);
+  Elf_Sym_Range getGlobalSymbols();
 
 protected:
-  llvm::object::ELFFile<ELFT> ELFObj;
-  const Elf_Shdr *Symtab = nullptr;
+  ArrayRef<Elf_Sym> Symbols;
+  uint32_t FirstNonLocal = 0;
   ArrayRef<Elf_Word> SymtabSHNDX;
   StringRef StringTable;
-  void initStringTable();
+  void initSymtab(ArrayRef<Elf_Shdr> Sections, const Elf_Shdr *Symtab);
 };
 
 // .o file.
 template <class ELFT> class ObjectFile : public ELFFileBase<ELFT> {
   typedef ELFFileBase<ELFT> Base;
+  typedef typename ELFT::Rel Elf_Rel;
+  typedef typename ELFT::Rela Elf_Rela;
   typedef typename ELFT::Sym Elf_Sym;
   typedef typename ELFT::Shdr Elf_Shdr;
   typedef typename ELFT::SymRange Elf_Sym_Range;
   typedef typename ELFT::Word Elf_Word;
   typedef typename ELFT::uint uintX_t;
 
-  StringRef getShtGroupSignature(const Elf_Shdr &Sec);
+  StringRef getShtGroupSignature(ArrayRef<Elf_Shdr> Sections,
+                                 const Elf_Shdr &Sec);
   ArrayRef<Elf_Word> getShtGroupEntries(const Elf_Shdr &Sec);
 
 public:
@@ -127,40 +143,49 @@ public:
   ArrayRef<SymbolBody *> getNonLocalSymbols();
 
   explicit ObjectFile(MemoryBufferRef M);
-  void parse(llvm::DenseSet<StringRef> &ComdatGroups);
+  void parse(llvm::DenseSet<llvm::CachedHashStringRef> &ComdatGroups);
 
   ArrayRef<InputSectionBase<ELFT> *> getSections() const { return Sections; }
   InputSectionBase<ELFT> *getSection(const Elf_Sym &Sym) const;
 
   SymbolBody &getSymbolBody(uint32_t SymbolIndex) const {
+    if (SymbolIndex >= SymbolBodies.size())
+      fatal(toString(this) + ": invalid symbol index");
     return *SymbolBodies[SymbolIndex];
   }
 
-  template <typename RelT> SymbolBody &getRelocTargetSym(const RelT &Rel) const {
+  template <typename RelT>
+  SymbolBody &getRelocTargetSym(const RelT &Rel) const {
     uint32_t SymIndex = Rel.getSymbol(Config->Mips64EL);
     return getSymbolBody(SymIndex);
   }
 
-  const Elf_Shdr *getSymbolTable() const { return this->Symtab; };
+  // Returns source line information for a given offset.
+  // If no information is available, returns "".
+  std::string getLineInfo(InputSectionBase<ELFT> *S, uintX_t Offset);
 
-  // Get MIPS GP0 value defined by this file. This value represents the gp value
+  // MIPS GP0 value defined by this file. This value represents the gp value
   // used to create the relocatable object and required to support
   // R_MIPS_GPREL16 / R_MIPS_GPREL32 relocations.
-  uint32_t getMipsGp0() const;
+  uint32_t MipsGp0 = 0;
 
   // The number is the offset in the string table. It will be used as the
   // st_name of the symbol.
   std::vector<std::pair<const DefinedRegular<ELFT> *, unsigned>> KeptLocalSyms;
 
-  // SymbolBodies and Thunks for sections in this file are allocated
-  // using this buffer.
-  llvm::BumpPtrAllocator Alloc;
+  // Name of source file obtained from STT_FILE symbol value,
+  // or empty string if there is no such symbol in object file
+  // symbol table.
+  StringRef SourceFile;
 
 private:
-  void initializeSections(llvm::DenseSet<StringRef> &ComdatGroups);
+  void
+  initializeSections(llvm::DenseSet<llvm::CachedHashStringRef> &ComdatGroups);
   void initializeSymbols();
+  void initializeDwarfLine();
   InputSectionBase<ELFT> *getRelocTarget(const Elf_Shdr &Sec);
-  InputSectionBase<ELFT> *createInputSection(const Elf_Shdr &Sec);
+  InputSectionBase<ELFT> *createInputSection(const Elf_Shdr &Sec,
+                                             StringRef SectionStringTable);
 
   bool shouldMerge(const Elf_Shdr &Sec);
   SymbolBody *createSymbolBody(const Elf_Sym *Sym);
@@ -171,14 +196,11 @@ private:
   // List of all symbols referenced or defined by this file.
   std::vector<SymbolBody *> SymbolBodies;
 
-  // MIPS .reginfo section defined by this file.
-  std::unique_ptr<MipsReginfoInputSection<ELFT>> MipsReginfo;
-  // MIPS .MIPS.options section defined by this file.
-  std::unique_ptr<MipsOptionsInputSection<ELFT>> MipsOptions;
-
-  llvm::SpecificBumpPtrAllocator<InputSection<ELFT>> IAlloc;
-  llvm::SpecificBumpPtrAllocator<MergeInputSection<ELFT>> MAlloc;
-  llvm::SpecificBumpPtrAllocator<EhInputSection<ELFT>> EHAlloc;
+  // Debugging information to retrieve source file and line for error
+  // reporting. Linker may find reasonable number of errors in a
+  // single object file, so we cache debugging information in order to
+  // parse it only once for each object file we link.
+  std::unique_ptr<llvm::DWARFDebugLine> DwarfLine;
 };
 
 // LazyObjectFile is analogous to ArchiveFile in the sense that
@@ -204,8 +226,6 @@ private:
   template <class ELFT> std::vector<StringRef> getElfSymbols();
   std::vector<StringRef> getBitcodeSymbols();
 
-  llvm::BumpPtrAllocator Alloc;
-  llvm::StringSaver Saver{Alloc};
   bool Seen = false;
 };
 
@@ -216,10 +236,11 @@ public:
   static bool classof(const InputFile *F) { return F->kind() == ArchiveKind; }
   template <class ELFT> void parse();
 
-  // Returns a memory buffer for a given symbol. An empty memory buffer
+  // Returns a memory buffer for a given symbol and the offset in the archive
+  // for the member. An empty memory buffer and an offset of zero
   // is returned if we have already returned the same memory buffer.
   // (So that we don't instantiate same members more than once.)
-  MemoryBufferRef getMember(const Archive::Symbol *Sym);
+  std::pair<MemoryBufferRef, uint64_t> getMember(const Archive::Symbol *Sym);
 
 private:
   std::unique_ptr<Archive> File;
@@ -231,30 +252,25 @@ public:
   explicit BitcodeFile(MemoryBufferRef M);
   static bool classof(const InputFile *F) { return F->kind() == BitcodeKind; }
   template <class ELFT>
-  void parse(llvm::DenseSet<StringRef> &ComdatGroups);
+  void parse(llvm::DenseSet<llvm::CachedHashStringRef> &ComdatGroups);
   ArrayRef<Symbol *> getSymbols() { return Symbols; }
-  static bool shouldSkip(uint32_t Flags);
-  std::unique_ptr<llvm::object::IRObjectFile> Obj;
+  std::unique_ptr<llvm::lto::InputFile> Obj;
 
 private:
   std::vector<Symbol *> Symbols;
-  llvm::BumpPtrAllocator Alloc;
-  llvm::StringSaver Saver{Alloc};
-  template <class ELFT>
-  Symbol *createSymbol(const llvm::DenseSet<const llvm::Comdat *> &KeptComdats,
-                       const llvm::object::IRObjectFile &Obj,
-                       const llvm::object::BasicSymbolRef &Sym);
 };
 
 // .so file.
 template <class ELFT> class SharedFile : public ELFFileBase<ELFT> {
   typedef ELFFileBase<ELFT> Base;
+  typedef typename ELFT::Dyn Elf_Dyn;
   typedef typename ELFT::Shdr Elf_Shdr;
   typedef typename ELFT::Sym Elf_Sym;
-  typedef typename ELFT::Word Elf_Word;
   typedef typename ELFT::SymRange Elf_Sym_Range;
-  typedef typename ELFT::Versym Elf_Versym;
   typedef typename ELFT::Verdef Elf_Verdef;
+  typedef typename ELFT::Versym Elf_Versym;
+  typedef typename ELFT::Word Elf_Word;
+  typedef typename ELFT::uint uintX_t;
 
   std::vector<StringRef> Undefs;
   StringRef SoName;
@@ -294,9 +310,20 @@ public:
   bool isNeeded() const { return !AsNeeded || IsUsed; }
 };
 
-std::unique_ptr<InputFile> createObjectFile(MemoryBufferRef MB,
-                                            StringRef ArchiveName = "");
-std::unique_ptr<InputFile> createSharedFile(MemoryBufferRef MB);
+class BinaryFile : public InputFile {
+public:
+  explicit BinaryFile(MemoryBufferRef M) : InputFile(BinaryKind, M) {}
+  static bool classof(const InputFile *F) { return F->kind() == BinaryKind; }
+  template <class ELFT> void parse();
+  ArrayRef<InputSectionData *> getSections() const { return Sections; }
+
+private:
+  std::vector<InputSectionData *> Sections;
+};
+
+InputFile *createObjectFile(MemoryBufferRef MB, StringRef ArchiveName = "",
+                            uint64_t OffsetInArchive = 0);
+InputFile *createSharedFile(MemoryBufferRef MB);
 
 } // namespace elf
 } // namespace lld
diff --git a/ELF/InputSection.cpp b/ELF/InputSection.cpp
index 6564e7995a89..805e51dab507 100644
--- a/ELF/InputSection.cpp
+++ b/ELF/InputSection.cpp
@@ -13,103 +13,187 @@
 #include "Error.h"
 #include "InputFiles.h"
 #include "LinkerScript.h"
+#include "Memory.h"
 #include "OutputSections.h"
+#include "Relocations.h"
+#include "SyntheticSections.h"
 #include "Target.h"
 #include "Thunks.h"
-
 #include "llvm/Support/Compression.h"
 #include "llvm/Support/Endian.h"
+#include <mutex>
 
 using namespace llvm;
 using namespace llvm::ELF;
 using namespace llvm::object;
+using namespace llvm::support;
 using namespace llvm::support::endian;
 
 using namespace lld;
 using namespace lld::elf;
 
-template <class ELFT> bool elf::isDiscarded(InputSectionBase<ELFT> *S) {
-  return !S || S == &InputSection<ELFT>::Discarded || !S->Live ||
-         Script<ELFT>::X->isDiscarded(S);
+// Returns a string to construct an error message.
+template <class ELFT>
+std::string elf::toString(const InputSectionBase<ELFT> *Sec) {
+  return (Sec->getFile()->getName() + ":(" + Sec->Name + ")").str();
+}
+
+template <class ELFT>
+static ArrayRef<uint8_t> getSectionContents(elf::ObjectFile<ELFT> *File,
+                                            const typename ELFT::Shdr *Hdr) {
+  if (!File || Hdr->sh_type == SHT_NOBITS)
+    return makeArrayRef<uint8_t>(nullptr, Hdr->sh_size);
+  return check(File->getObj().getSectionContents(Hdr));
 }
 
 template <class ELFT>
 InputSectionBase<ELFT>::InputSectionBase(elf::ObjectFile<ELFT> *File,
-                                         const Elf_Shdr *Header,
+                                         uintX_t Flags, uint32_t Type,
+                                         uintX_t Entsize, uint32_t Link,
+                                         uint32_t Info, uintX_t Addralign,
+                                         ArrayRef<uint8_t> Data, StringRef Name,
                                          Kind SectionKind)
-    : Header(Header), File(File), SectionKind(SectionKind), Repl(this),
-      Compressed(Header->sh_flags & SHF_COMPRESSED) {
-  // The garbage collector sets sections' Live bits.
-  // If GC is disabled, all sections are considered live by default.
-  Live = !Config->GcSections;
+    : InputSectionData(SectionKind, Name, Data,
+                       !Config->GcSections || !(Flags & SHF_ALLOC)),
+      File(File), Flags(Flags), Entsize(Entsize), Type(Type), Link(Link),
+      Info(Info), Repl(this) {
+  NumRelocations = 0;
+  AreRelocsRela = false;
 
   // The ELF spec states that a value of 0 means the section has
   // no alignment constraits.
-  Alignment = std::max<uintX_t>(Header->sh_addralign, 1);
+  uint64_t V = std::max<uint64_t>(Addralign, 1);
+  if (!isPowerOf2_64(V))
+    fatal(toString(File) + ": section sh_addralign is not a power of 2");
+
+  // We reject object files having insanely large alignments even though
+  // they are allowed by the spec. I think 4GB is a reasonable limitation.
+  // We might want to relax this in the future.
+  if (V > UINT32_MAX)
+    fatal(toString(File) + ": section sh_addralign is too large");
+  Alignment = V;
+
+  // If it is not a mergeable section, overwrite the flag so that the flag
+  // is consistent with the class. This inconsistency could occur when
+  // string merging is disabled using -O0 flag.
+  if (!Config->Relocatable && !isa<MergeInputSection<ELFT>>(this))
+    this->Flags &= ~(SHF_MERGE | SHF_STRINGS);
+}
+
+template <class ELFT>
+InputSectionBase<ELFT>::InputSectionBase(elf::ObjectFile<ELFT> *File,
+                                         const Elf_Shdr *Hdr, StringRef Name,
+                                         Kind SectionKind)
+    : InputSectionBase(File, Hdr->sh_flags & ~SHF_INFO_LINK, Hdr->sh_type,
+                       Hdr->sh_entsize, Hdr->sh_link, Hdr->sh_info,
+                       Hdr->sh_addralign, getSectionContents(File, Hdr), Name,
+                       SectionKind) {
+  this->Offset = Hdr->sh_offset;
 }
 
 template <class ELFT> size_t InputSectionBase<ELFT>::getSize() const {
+  if (auto *S = dyn_cast<SyntheticSection<ELFT>>(this))
+    return S->getSize();
+
   if (auto *D = dyn_cast<InputSection<ELFT>>(this))
     if (D->getThunksSize() > 0)
       return D->getThunkOff() + D->getThunksSize();
-  return Header->sh_size;
-}
 
-template <class ELFT> StringRef InputSectionBase<ELFT>::getSectionName() const {
-  return check(File->getObj().getSectionName(this->Header));
+  return Data.size();
 }
 
-template <class ELFT>
-ArrayRef<uint8_t> InputSectionBase<ELFT>::getSectionData() const {
-  if (Compressed)
-    return ArrayRef<uint8_t>((const uint8_t *)Uncompressed.data(),
-                             Uncompressed.size());
-  return check(this->File->getObj().getSectionContents(this->Header));
+// Returns a string for an error message.
+template <class SectionT> static std::string getName(SectionT *Sec) {
+  return (Sec->getFile()->getName() + ":(" + Sec->Name + ")").str();
 }
 
 template <class ELFT>
 typename ELFT::uint InputSectionBase<ELFT>::getOffset(uintX_t Offset) const {
-  switch (SectionKind) {
+  switch (kind()) {
   case Regular:
     return cast<InputSection<ELFT>>(this)->OutSecOff + Offset;
+  case Synthetic:
+    // For synthetic sections we treat offset -1 as the end of the section.
+    // The same approach is used for synthetic symbols (DefinedSynthetic).
+    return cast<InputSection<ELFT>>(this)->OutSecOff +
+           (Offset == uintX_t(-1) ? getSize() : Offset);
   case EHFrame:
-    return cast<EhInputSection<ELFT>>(this)->getOffset(Offset);
+    // The file crtbeginT.o has relocations pointing to the start of an empty
+    // .eh_frame that is known to be the first in the link. It does that to
+    // identify the start of the output .eh_frame.
+    return Offset;
   case Merge:
     return cast<MergeInputSection<ELFT>>(this)->getOffset(Offset);
-  case MipsReginfo:
-  case MipsOptions:
-    // MIPS .reginfo and .MIPS.options sections are consumed by the linker,
-    // and the linker produces a single output section. It is possible that
-    // input files contain section symbol points to the corresponding input
-    // section. Redirect it to the produced output section.
-    if (Offset != 0)
-      fatal("Unsupported reference to the middle of '" + getSectionName() +
-            "' section");
-    return this->OutSec->getVA();
   }
   llvm_unreachable("invalid section kind");
 }
 
-template <class ELFT> void InputSectionBase<ELFT>::uncompress() {
-  if (!zlib::isAvailable())
-    fatal("build lld with zlib to enable compressed sections support");
+template <class ELFT> bool InputSectionBase<ELFT>::isCompressed() const {
+  return (Flags & SHF_COMPRESSED) || Name.startswith(".zdebug");
+}
 
-  // A compressed section consists of a header of Elf_Chdr type
-  // followed by compressed data.
-  ArrayRef<uint8_t> Data =
-      check(this->File->getObj().getSectionContents(this->Header));
+// Returns compressed data and its size when uncompressed.
+template <class ELFT>
+std::pair<ArrayRef<uint8_t>, uint64_t>
+InputSectionBase<ELFT>::getElfCompressedData(ArrayRef<uint8_t> Data) {
+  // Compressed section with Elf_Chdr is the ELF standard.
   if (Data.size() < sizeof(Elf_Chdr))
-    fatal("corrupt compressed section");
-
+    fatal(toString(this) + ": corrupted compressed section");
   auto *Hdr = reinterpret_cast<const Elf_Chdr *>(Data.data());
-  Data = Data.slice(sizeof(Elf_Chdr));
-
   if (Hdr->ch_type != ELFCOMPRESS_ZLIB)
-    fatal("unsupported compression type");
+    fatal(toString(this) + ": unsupported compression type");
+  return {Data.slice(sizeof(*Hdr)), Hdr->ch_size};
+}
 
-  StringRef Buf((const char *)Data.data(), Data.size());
-  if (zlib::uncompress(Buf, Uncompressed, Hdr->ch_size) != zlib::StatusOK)
-    fatal("error uncompressing section");
+// Returns compressed data and its size when uncompressed.
+template <class ELFT>
+std::pair<ArrayRef<uint8_t>, uint64_t>
+InputSectionBase<ELFT>::getRawCompressedData(ArrayRef<uint8_t> Data) {
+  // Compressed sections without Elf_Chdr header contain this header
+  // instead. This is a GNU extension.
+  struct ZlibHeader {
+    char Magic[4]; // Should be "ZLIB"
+    char Size[8];  // Uncompressed size in big-endian
+  };
+
+  if (Data.size() < sizeof(ZlibHeader))
+    fatal(toString(this) + ": corrupted compressed section");
+  auto *Hdr = reinterpret_cast<const ZlibHeader *>(Data.data());
+  if (memcmp(Hdr->Magic, "ZLIB", 4))
+    fatal(toString(this) + ": broken ZLIB-compressed section");
+  return {Data.slice(sizeof(*Hdr)), read64be(Hdr->Size)};
+}
+
+// Uncompress section contents. Note that this function is called
+// from parallel_for_each, so it must be thread-safe.
+template <class ELFT> void InputSectionBase<ELFT>::uncompress() {
+  if (!zlib::isAvailable())
+    fatal(toString(this) +
+          ": build lld with zlib to enable compressed sections support");
+
+  // This section is compressed. Here we decompress it. Ideally, all
+  // compressed sections have SHF_COMPRESSED bit and their contents
+  // start with headers of Elf_Chdr type. However, sections whose
+  // names start with ".zdebug_" don't have the bit and contains a raw
+  // ZLIB-compressed data (which is a bad thing because section names
+  // shouldn't be significant in ELF.) We need to be able to read both.
+  ArrayRef<uint8_t> Buf; // Compressed data
+  size_t Size;           // Uncompressed size
+  if (Flags & SHF_COMPRESSED)
+    std::tie(Buf, Size) = getElfCompressedData(Data);
+  else
+    std::tie(Buf, Size) = getRawCompressedData(Data);
+
+  // Uncompress Buf.
+  char *OutputBuf;
+  {
+    static std::mutex Mu;
+    std::lock_guard<std::mutex> Lock(Mu);
+    OutputBuf = BAlloc.Allocate<char>(Size);
+  }
+  if (zlib::uncompress(toStringRef(Buf), OutputBuf, Size) != zlib::StatusOK)
+    fatal(toString(this) + ": error while uncompressing section");
+  Data = ArrayRef<uint8_t>((uint8_t *)OutputBuf, Size);
 }
 
 template <class ELFT>
@@ -119,29 +203,71 @@ InputSectionBase<ELFT>::getOffset(const DefinedRegular<ELFT> &Sym) const {
 }
 
 template <class ELFT>
+InputSectionBase<ELFT> *InputSectionBase<ELFT>::getLinkOrderDep() const {
+  if ((Flags & SHF_LINK_ORDER) && Link != 0)
+    return getFile()->getSections()[Link];
+  return nullptr;
+}
+
+// Returns a source location string. Used to construct an error message.
+template <class ELFT>
+std::string InputSectionBase<ELFT>::getLocation(typename ELFT::uint Offset) {
+  // First check if we can get desired values from debugging information.
+  std::string LineInfo = File->getLineInfo(this, Offset);
+  if (!LineInfo.empty())
+    return LineInfo;
+
+  // File->SourceFile contains STT_FILE symbol that contains a
+  // source file name. If it's missing, we use an object file name.
+  std::string SrcFile = File->SourceFile;
+  if (SrcFile.empty())
+    SrcFile = toString(File);
+
+  // Find a function symbol that encloses a given location.
+  for (SymbolBody *B : File->getSymbols())
+    if (auto *D = dyn_cast<DefinedRegular<ELFT>>(B))
+      if (D->Section == this && D->Type == STT_FUNC)
+        if (D->Value <= Offset && Offset < D->Value + D->Size)
+          return SrcFile + ":(function " + toString(*D) + ")";
+
+  // If there's no symbol, print out the offset in the section.
+  return (SrcFile + ":(" + Name + "+0x" + utohexstr(Offset) + ")").str();
+}
+
+template <class ELFT>
+InputSection<ELFT>::InputSection() : InputSectionBase<ELFT>() {}
+
+template <class ELFT>
+InputSection<ELFT>::InputSection(uintX_t Flags, uint32_t Type,
+                                 uintX_t Addralign, ArrayRef<uint8_t> Data,
+                                 StringRef Name, Kind K)
+    : InputSectionBase<ELFT>(nullptr, Flags, Type,
+                             /*Entsize*/ 0, /*Link*/ 0, /*Info*/ 0, Addralign,
+                             Data, Name, K) {}
+
+template <class ELFT>
 InputSection<ELFT>::InputSection(elf::ObjectFile<ELFT> *F,
-                                 const Elf_Shdr *Header)
-    : InputSectionBase<ELFT>(F, Header, Base::Regular) {}
+                                 const Elf_Shdr *Header, StringRef Name)
+    : InputSectionBase<ELFT>(F, Header, Name, Base::Regular) {}
 
 template <class ELFT>
-bool InputSection<ELFT>::classof(const InputSectionBase<ELFT> *S) {
-  return S->SectionKind == Base::Regular;
+bool InputSection<ELFT>::classof(const InputSectionData *S) {
+  return S->kind() == Base::Regular || S->kind() == Base::Synthetic;
 }
 
 template <class ELFT>
 InputSectionBase<ELFT> *InputSection<ELFT>::getRelocatedSection() {
-  assert(this->Header->sh_type == SHT_RELA || this->Header->sh_type == SHT_REL);
+  assert(this->Type == SHT_RELA || this->Type == SHT_REL);
   ArrayRef<InputSectionBase<ELFT> *> Sections = this->File->getSections();
-  return Sections[this->Header->sh_info];
+  return Sections[this->Info];
 }
 
-template <class ELFT>
-void InputSection<ELFT>::addThunk(const Thunk<ELFT> *T) {
+template <class ELFT> void InputSection<ELFT>::addThunk(const Thunk<ELFT> *T) {
   Thunks.push_back(T);
 }
 
 template <class ELFT> uint64_t InputSection<ELFT>::getThunkOff() const {
-  return this->Header->sh_size;
+  return this->Data.size();
 }
 
 template <class ELFT> uint64_t InputSection<ELFT>::getThunksSize() const {
@@ -163,35 +289,62 @@ void InputSection<ELFT>::copyRelocations(uint8_t *Buf, ArrayRef<RelTy> Rels) {
     uint32_t Type = Rel.getType(Config->Mips64EL);
     SymbolBody &Body = this->File->getRelocTargetSym(Rel);
 
-    RelTy *P = reinterpret_cast<RelTy *>(Buf);
+    Elf_Rela *P = reinterpret_cast<Elf_Rela *>(Buf);
     Buf += sizeof(RelTy);
 
+    if (Config->Rela)
+      P->r_addend = getAddend<ELFT>(Rel);
     P->r_offset = RelocatedSection->getOffset(Rel.r_offset);
     P->setSymbolAndType(Body.DynsymIndex, Type, Config->Mips64EL);
   }
 }
 
-// Page(Expr) is the page address of the expression Expr, defined
-// as (Expr & ~0xFFF). (This applies even if the machine page size
-// supported by the platform has a different value.)
-static uint64_t getAArch64Page(uint64_t Expr) {
-  return Expr & (~static_cast<uint64_t>(0xFFF));
+static uint32_t getARMUndefinedRelativeWeakVA(uint32_t Type, uint32_t A,
+                                              uint32_t P) {
+  switch (Type) {
+  case R_ARM_THM_JUMP11:
+    return P + 2;
+  case R_ARM_CALL:
+  case R_ARM_JUMP24:
+  case R_ARM_PC24:
+  case R_ARM_PLT32:
+  case R_ARM_PREL31:
+  case R_ARM_THM_JUMP19:
+  case R_ARM_THM_JUMP24:
+    return P + 4;
+  case R_ARM_THM_CALL:
+    // We don't want an interworking BLX to ARM
+    return P + 5;
+  default:
+    return A;
+  }
 }
 
-template <class ELFT>
-static typename ELFT::uint getSymVA(uint32_t Type, typename ELFT::uint A,
-                                    typename ELFT::uint P,
-                                    const SymbolBody &Body, RelExpr Expr) {
-  typedef typename ELFT::uint uintX_t;
+static uint64_t getAArch64UndefinedRelativeWeakVA(uint64_t Type, uint64_t A,
+                                                  uint64_t P) {
+  switch (Type) {
+  case R_AARCH64_CALL26:
+  case R_AARCH64_CONDBR19:
+  case R_AARCH64_JUMP26:
+  case R_AARCH64_TSTBR14:
+    return P + 4;
+  default:
+    return A;
+  }
+}
 
+template <class ELFT>
+static typename ELFT::uint
+getRelocTargetVA(uint32_t Type, typename ELFT::uint A, typename ELFT::uint P,
+                 const SymbolBody &Body, RelExpr Expr) {
   switch (Expr) {
   case R_HINT:
+  case R_TLSDESC_CALL:
     llvm_unreachable("cannot relocate hint relocs");
   case R_TLSLD:
-    return Out<ELFT>::Got->getTlsIndexOff() + A -
-           Out<ELFT>::Got->getNumEntries() * sizeof(uintX_t);
+    return In<ELFT>::Got->getTlsIndexOff() + A - In<ELFT>::Got->getSize();
   case R_TLSLD_PC:
-    return Out<ELFT>::Got->getTlsIndexVA() + A - P;
+    return In<ELFT>::Got->getTlsIndexVA() + A - P;
   case R_THUNK_ABS:
     return Body.getThunkVA<ELFT>() + A;
   case R_THUNK_PC:
@@ -200,14 +353,14 @@ static typename ELFT::uint getSymVA(uint32_t Type, typename ELFT::uint A,
   case R_PPC_TOC:
     return getPPC64TocBase() + A;
   case R_TLSGD:
-    return Out<ELFT>::Got->getGlobalDynOffset(Body) + A -
-           Out<ELFT>::Got->getNumEntries() * sizeof(uintX_t);
+    return In<ELFT>::Got->getGlobalDynOffset(Body) + A -
+           In<ELFT>::Got->getSize();
   case R_TLSGD_PC:
-    return Out<ELFT>::Got->getGlobalDynAddr(Body) + A - P;
+    return In<ELFT>::Got->getGlobalDynAddr(Body) + A - P;
   case R_TLSDESC:
-    return Out<ELFT>::Got->getGlobalDynAddr(Body) + A;
+    return In<ELFT>::Got->getGlobalDynAddr(Body) + A;
   case R_TLSDESC_PAGE:
-    return getAArch64Page(Out<ELFT>::Got->getGlobalDynAddr(Body) + A) -
+    return getAArch64Page(In<ELFT>::Got->getGlobalDynAddr(Body) + A) -
            getAArch64Page(P);
   case R_PLT:
     return Body.getPltVA<ELFT>() + A;
@@ -217,11 +370,13 @@ static typename ELFT::uint getSymVA(uint32_t Type, typename ELFT::uint A,
   case R_SIZE:
     return Body.getSize<ELFT>() + A;
   case R_GOTREL:
-    return Body.getVA<ELFT>(A) - Out<ELFT>::Got->getVA();
+    return Body.getVA<ELFT>(A) - In<ELFT>::Got->getVA();
+  case R_GOTREL_FROM_END:
+    return Body.getVA<ELFT>(A) - In<ELFT>::Got->getVA() -
+           In<ELFT>::Got->getSize();
   case R_RELAX_TLS_GD_TO_IE_END:
   case R_GOT_FROM_END:
-    return Body.getGotOffset<ELFT>() + A -
-           Out<ELFT>::Got->getNumEntries() * sizeof(uintX_t);
+    return Body.getGotOffset<ELFT>() + A - In<ELFT>::Got->getSize();
   case R_RELAX_TLS_GD_TO_IE_ABS:
   case R_GOT:
     return Body.getGotVA<ELFT>() + A;
@@ -232,11 +387,21 @@ static typename ELFT::uint getSymVA(uint32_t Type, typename ELFT::uint A,
   case R_GOT_PC:
     return Body.getGotVA<ELFT>() + A - P;
   case R_GOTONLY_PC:
-    return Out<ELFT>::Got->getVA() + A - P;
+    return In<ELFT>::Got->getVA() + A - P;
+  case R_GOTONLY_PC_FROM_END:
+    return In<ELFT>::Got->getVA() + A - P + In<ELFT>::Got->getSize();
   case R_RELAX_TLS_LD_TO_LE:
   case R_RELAX_TLS_IE_TO_LE:
   case R_RELAX_TLS_GD_TO_LE:
   case R_TLS:
+    // A weak undefined TLS symbol resolves to the base of the TLS
+    // block, i.e. gets a value of zero. If we pass --gc-sections to
+    // lld and .tbss is not referenced, it gets reclaimed and we don't
+    // create a TLS program header. Therefore, we resolve this
+    // statically to zero.
+    if (Body.isTls() && (Body.isLazy() || Body.isUndefined()) &&
+        Body.symbol()->isWeak())
+      return 0;
     if (Target->TcbSize)
       return Body.getVA<ELFT>(A) +
              alignTo(Target->TcbSize, Out<ELFT>::TlsPhdr->p_align);
@@ -253,18 +418,26 @@ static typename ELFT::uint getSymVA(uint32_t Type, typename ELFT::uint A,
     // If relocation against MIPS local symbol requires GOT entry, this entry
     // should be initialized by 'page address'. This address is high 16-bits
     // of sum the symbol's value and the addend.
-    return Out<ELFT>::Got->getMipsLocalPageOffset(Body.getVA<ELFT>(A));
+    return In<ELFT>::MipsGot->getVA() +
+           In<ELFT>::MipsGot->getPageEntryOffset(Body, A) -
+           In<ELFT>::MipsGot->getGp();
   case R_MIPS_GOT_OFF:
+  case R_MIPS_GOT_OFF32:
     // In case of MIPS if a GOT relocation has non-zero addend this addend
     // should be applied to the GOT entry content not to the GOT entry offset.
     // That is why we use separate expression type.
-    return Out<ELFT>::Got->getMipsGotOffset(Body, A);
+    return In<ELFT>::MipsGot->getVA() +
+           In<ELFT>::MipsGot->getBodyEntryOffset(Body, A) -
+           In<ELFT>::MipsGot->getGp();
+  case R_MIPS_GOTREL:
+    return Body.getVA<ELFT>(A) - In<ELFT>::MipsGot->getGp();
   case R_MIPS_TLSGD:
-    return Out<ELFT>::Got->getGlobalDynOffset(Body) +
-           Out<ELFT>::Got->getMipsTlsOffset() - MipsGPOffset;
+    return In<ELFT>::MipsGot->getVA() + In<ELFT>::MipsGot->getTlsOffset() +
+           In<ELFT>::MipsGot->getGlobalDynOffset(Body) -
+           In<ELFT>::MipsGot->getGp();
   case R_MIPS_TLSLD:
-    return Out<ELFT>::Got->getTlsIndexOff() +
-           Out<ELFT>::Got->getMipsTlsOffset() - MipsGPOffset;
+    return In<ELFT>::MipsGot->getVA() + In<ELFT>::MipsGot->getTlsOffset() +
+           In<ELFT>::MipsGot->getTlsIndexOff() - In<ELFT>::MipsGot->getGp();
   case R_PPC_OPD: {
     uint64_t SymVA = Body.getVA<ELFT>(A);
     // If we have an undefined weak symbol, we might get here with a symbol
@@ -275,8 +448,8 @@ static typename ELFT::uint getSymVA(uint32_t Type, typename ELFT::uint A,
     if (Out<ELF64BE>::Opd) {
       // If this is a local call, and we currently have the address of a
       // function-descriptor, get the underlying code address instead.
-      uint64_t OpdStart = Out<ELF64BE>::Opd->getVA();
-      uint64_t OpdEnd = OpdStart + Out<ELF64BE>::Opd->getSize();
+      uint64_t OpdStart = Out<ELF64BE>::Opd->Addr;
+      uint64_t OpdEnd = OpdStart + Out<ELF64BE>::Opd->Size;
       bool InOpd = OpdStart <= SymVA && SymVA < OpdEnd;
       if (InOpd)
         SymVA = read64be(&Out<ELF64BE>::OpdBuf[SymVA - OpdStart]);
@@ -284,10 +457,20 @@ static typename ELFT::uint getSymVA(uint32_t Type, typename ELFT::uint A,
     return SymVA - P;
   }
   case R_PC:
+    if (Body.isUndefined() && !Body.isLocal() && Body.symbol()->isWeak()) {
+      // On ARM and AArch64 a branch to an undefined weak resolves to the
+      // next instruction, otherwise the place.
+      if (Config->EMachine == EM_ARM)
+        return getARMUndefinedRelativeWeakVA(Type, A, P);
+      if (Config->EMachine == EM_AARCH64)
+        return getAArch64UndefinedRelativeWeakVA(Type, A, P);
+    }
   case R_RELAX_GOT_PC:
     return Body.getVA<ELFT>(A) - P;
   case R_PLT_PAGE_PC:
   case R_PAGE_PC:
+    if (Body.isUndefined() && !Body.isLocal() && Body.symbol()->isWeak())
+      return getAArch64Page(A);
     return getAArch64Page(Body.getVA<ELFT>(A)) - getAArch64Page(P);
   }
   llvm_unreachable("Invalid expression");
@@ -303,7 +486,6 @@ static typename ELFT::uint getSymVA(uint32_t Type, typename ELFT::uint A,
 template <class ELFT>
 template <class RelTy>
 void InputSection<ELFT>::relocateNonAlloc(uint8_t *Buf, ArrayRef<RelTy> Rels) {
-  const unsigned Bits = sizeof(uintX_t) * 8;
   for (const RelTy &Rel : Rels) {
     uint32_t Type = Rel.getType(Config->Mips64EL);
     uintX_t Offset = this->getOffset(Rel.r_offset);
@@ -314,13 +496,15 @@ void InputSection<ELFT>::relocateNonAlloc(uint8_t *Buf, ArrayRef<RelTy> Rels) {
 
     SymbolBody &Sym = this->File->getRelocTargetSym(Rel);
     if (Target->getRelExpr(Type, Sym) != R_ABS) {
-      error(this->getSectionName() + " has non-ABS reloc");
+      error(this->getLocation(Offset) + ": has non-ABS reloc");
       return;
     }
 
-    uintX_t AddrLoc = this->OutSec->getVA() + Offset;
-    uint64_t SymVA =
-        SignExtend64<Bits>(getSymVA<ELFT>(Type, Addend, AddrLoc, Sym, R_ABS));
+    uintX_t AddrLoc = this->OutSec->Addr + Offset;
+    uint64_t SymVA = 0;
+    if (!Sym.isTls() || Out<ELFT>::TlsPhdr)
+      SymVA = SignExtend64<sizeof(uintX_t) * 8>(
+          getRelocTargetVA<ELFT>(Type, Addend, AddrLoc, Sym, R_ABS));
     Target->relocateOne(BufLoc, Type, SymVA);
   }
 }
@@ -331,78 +515,80 @@ void InputSectionBase<ELFT>::relocate(uint8_t *Buf, uint8_t *BufEnd) {
   // vector only for SHF_ALLOC'ed sections. For other sections,
   // we handle relocations directly here.
   auto *IS = dyn_cast<InputSection<ELFT>>(this);
-  if (IS && !(IS->Header->sh_flags & SHF_ALLOC)) {
-    for (const Elf_Shdr *RelSec : IS->RelocSections) {
-      if (RelSec->sh_type == SHT_RELA)
-        IS->relocateNonAlloc(Buf, IS->File->getObj().relas(RelSec));
-      else
-        IS->relocateNonAlloc(Buf, IS->File->getObj().rels(RelSec));
-    }
+  if (IS && !(IS->Flags & SHF_ALLOC)) {
+    if (IS->AreRelocsRela)
+      IS->relocateNonAlloc(Buf, IS->relas());
+    else
+      IS->relocateNonAlloc(Buf, IS->rels());
     return;
   }
 
   const unsigned Bits = sizeof(uintX_t) * 8;
-  for (const Relocation<ELFT> &Rel : Relocations) {
-    uintX_t Offset = Rel.InputSec->getOffset(Rel.Offset);
+  for (const Relocation &Rel : Relocations) {
+    uintX_t Offset = getOffset(Rel.Offset);
     uint8_t *BufLoc = Buf + Offset;
     uint32_t Type = Rel.Type;
     uintX_t A = Rel.Addend;
 
-    uintX_t AddrLoc = OutSec->getVA() + Offset;
+    uintX_t AddrLoc = OutSec->Addr + Offset;
     RelExpr Expr = Rel.Expr;
-    uint64_t SymVA =
-        SignExtend64<Bits>(getSymVA<ELFT>(Type, A, AddrLoc, *Rel.Sym, Expr));
+    uint64_t TargetVA = SignExtend64<Bits>(
+        getRelocTargetVA<ELFT>(Type, A, AddrLoc, *Rel.Sym, Expr));
 
     switch (Expr) {
     case R_RELAX_GOT_PC:
     case R_RELAX_GOT_PC_NOPIC:
-      Target->relaxGot(BufLoc, SymVA);
+      Target->relaxGot(BufLoc, TargetVA);
       break;
     case R_RELAX_TLS_IE_TO_LE:
-      Target->relaxTlsIeToLe(BufLoc, Type, SymVA);
+      Target->relaxTlsIeToLe(BufLoc, Type, TargetVA);
       break;
     case R_RELAX_TLS_LD_TO_LE:
-      Target->relaxTlsLdToLe(BufLoc, Type, SymVA);
+      Target->relaxTlsLdToLe(BufLoc, Type, TargetVA);
       break;
     case R_RELAX_TLS_GD_TO_LE:
     case R_RELAX_TLS_GD_TO_LE_NEG:
-      Target->relaxTlsGdToLe(BufLoc, Type, SymVA);
+      Target->relaxTlsGdToLe(BufLoc, Type, TargetVA);
       break;
     case R_RELAX_TLS_GD_TO_IE:
     case R_RELAX_TLS_GD_TO_IE_ABS:
     case R_RELAX_TLS_GD_TO_IE_PAGE_PC:
     case R_RELAX_TLS_GD_TO_IE_END:
-      Target->relaxTlsGdToIe(BufLoc, Type, SymVA);
+      Target->relaxTlsGdToIe(BufLoc, Type, TargetVA);
       break;
     case R_PPC_PLT_OPD:
       // Patch a nop (0x60000000) to a ld.
       if (BufLoc + 8 <= BufEnd && read32be(BufLoc + 4) == 0x60000000)
         write32be(BufLoc + 4, 0xe8410028); // ld %r2, 40(%r1)
-      // fallthrough
+    // fallthrough
     default:
-      Target->relocateOne(BufLoc, Type, SymVA);
+      Target->relocateOne(BufLoc, Type, TargetVA);
       break;
     }
   }
 }
 
 template <class ELFT> void InputSection<ELFT>::writeTo(uint8_t *Buf) {
-  if (this->Header->sh_type == SHT_NOBITS)
+  if (this->Type == SHT_NOBITS)
+    return;
+
+  if (auto *S = dyn_cast<SyntheticSection<ELFT>>(this)) {
+    S->writeTo(Buf + OutSecOff);
     return;
-  ELFFile<ELFT> &EObj = this->File->getObj();
+  }
 
   // If -r is given, then an InputSection may be a relocation section.
-  if (this->Header->sh_type == SHT_RELA) {
-    copyRelocations(Buf + OutSecOff, EObj.relas(this->Header));
+  if (this->Type == SHT_RELA) {
+    copyRelocations(Buf + OutSecOff, this->template getDataAs<Elf_Rela>());
     return;
   }
-  if (this->Header->sh_type == SHT_REL) {
-    copyRelocations(Buf + OutSecOff, EObj.rels(this->Header));
+  if (this->Type == SHT_REL) {
+    copyRelocations(Buf + OutSecOff, this->template getDataAs<Elf_Rel>());
     return;
   }
 
   // Copy section contents from source object file to output file.
-  ArrayRef<uint8_t> Data = this->getSectionData();
+  ArrayRef<uint8_t> Data = this->Data;
   memcpy(Buf + OutSecOff, Data.data(), Data.size());
 
   // Iterate over all relocation sections that apply to this section.
@@ -431,15 +617,9 @@ void InputSection<ELFT>::replace(InputSection<ELFT> *Other) {
 }
 
 template <class ELFT>
-SplitInputSection<ELFT>::SplitInputSection(
-    elf::ObjectFile<ELFT> *File, const Elf_Shdr *Header,
-    typename InputSectionBase<ELFT>::Kind SectionKind)
-    : InputSectionBase<ELFT>(File, Header, SectionKind) {}
-
-template <class ELFT>
 EhInputSection<ELFT>::EhInputSection(elf::ObjectFile<ELFT> *F,
-                                     const Elf_Shdr *Header)
-    : SplitInputSection<ELFT>(F, Header, InputSectionBase<ELFT>::EHFrame) {
+                                     const Elf_Shdr *Header, StringRef Name)
+    : InputSectionBase<ELFT>(F, Header, Name, InputSectionBase<ELFT>::EHFrame) {
   // Mark .eh_frame sections as live by default because there are
   // usually no relocations that point to .eh_frames. Otherwise,
   // the garbage collector would drop all .eh_frame sections.
@@ -447,18 +627,54 @@ EhInputSection<ELFT>::EhInputSection(elf::ObjectFile<ELFT> *F,
 }
 
 template <class ELFT>
-bool EhInputSection<ELFT>::classof(const InputSectionBase<ELFT> *S) {
-  return S->SectionKind == InputSectionBase<ELFT>::EHFrame;
+bool EhInputSection<ELFT>::classof(const InputSectionData *S) {
+  return S->kind() == InputSectionBase<ELFT>::EHFrame;
+}
+
+// Returns the index of the first relocation that points to a region between
+// Begin and Begin+Size.
+template <class IntTy, class RelTy>
+static unsigned getReloc(IntTy Begin, IntTy Size, const ArrayRef<RelTy> &Rels,
+                         unsigned &RelocI) {
+  // Start search from RelocI for fast access. That works because the
+  // relocations are sorted in .eh_frame.
+  for (unsigned N = Rels.size(); RelocI < N; ++RelocI) {
+    const RelTy &Rel = Rels[RelocI];
+    if (Rel.r_offset < Begin)
+      continue;
+
+    if (Rel.r_offset < Begin + Size)
+      return RelocI;
+    return -1;
+  }
+  return -1;
 }
 
 // .eh_frame is a sequence of CIE or FDE records.
 // This function splits an input section into records and returns them.
+template <class ELFT> void EhInputSection<ELFT>::split() {
+  // Early exit if already split.
+  if (!this->Pieces.empty())
+    return;
+
+  if (this->NumRelocations) {
+    if (this->AreRelocsRela)
+      split(this->relas());
+    else
+      split(this->rels());
+    return;
+  }
+  split(makeArrayRef<typename ELFT::Rela>(nullptr, nullptr));
+}
+
 template <class ELFT>
-void EhInputSection<ELFT>::split() {
-  ArrayRef<uint8_t> Data = this->getSectionData();
+template <class RelTy>
+void EhInputSection<ELFT>::split(ArrayRef<RelTy> Rels) {
+  ArrayRef<uint8_t> Data = this->Data;
+  unsigned RelI = 0;
   for (size_t Off = 0, End = Data.size(); Off != End;) {
-    size_t Size = readEhRecordSize<ELFT>(Data.slice(Off));
-    this->Pieces.emplace_back(Off, Data.slice(Off, Size));
+    size_t Size = readEhRecordSize<ELFT>(this, Off);
+    this->Pieces.emplace_back(Off, this, Size, getReloc(Off, Size, Rels, RelI));
     // The empty record is the end marker.
     if (Size == 4)
       break;
@@ -466,21 +682,6 @@ void EhInputSection<ELFT>::split() {
   }
 }
 
-template <class ELFT>
-typename ELFT::uint EhInputSection<ELFT>::getOffset(uintX_t Offset) const {
-  // The file crtbeginT.o has relocations pointing to the start of an empty
-  // .eh_frame that is known to be the first in the link. It does that to
-  // identify the start of the output .eh_frame. Handle this special case.
-  if (this->getSectionHdr()->sh_size == 0)
-    return Offset;
-  const SectionPiece *Piece = this->getSectionPiece(Offset);
-  if (Piece->OutputOff == size_t(-1))
-    return -1; // Not in the output
-
-  uintX_t Addend = Offset - Piece->InputOff;
-  return Piece->OutputOff + Addend;
-}
-
 static size_t findNull(ArrayRef<uint8_t> A, size_t EntSize) {
   // Optimize the common case.
   StringRef S((const char *)A.data(), A.size());
@@ -497,75 +698,96 @@ static size_t findNull(ArrayRef<uint8_t> A, size_t EntSize) {
 
 // Split SHF_STRINGS section. Such section is a sequence of
 // null-terminated strings.
-static std::vector<SectionPiece> splitStrings(ArrayRef<uint8_t> Data,
-                                              size_t EntSize) {
-  std::vector<SectionPiece> V;
+template <class ELFT>
+void MergeInputSection<ELFT>::splitStrings(ArrayRef<uint8_t> Data,
+                                           size_t EntSize) {
   size_t Off = 0;
+  bool IsAlloc = this->Flags & SHF_ALLOC;
   while (!Data.empty()) {
     size_t End = findNull(Data, EntSize);
     if (End == StringRef::npos)
-      fatal("string is not null terminated");
+      fatal(toString(this) + ": string is not null terminated");
     size_t Size = End + EntSize;
-    V.emplace_back(Off, Data.slice(0, Size));
+    Pieces.emplace_back(Off, !IsAlloc);
+    Hashes.push_back(hash_value(toStringRef(Data.slice(0, Size))));
     Data = Data.slice(Size);
     Off += Size;
   }
-  return V;
 }
 
 // Split non-SHF_STRINGS section. Such section is a sequence of
 // fixed size records.
-static std::vector<SectionPiece> splitNonStrings(ArrayRef<uint8_t> Data,
-                                                 size_t EntSize) {
-  std::vector<SectionPiece> V;
+template <class ELFT>
+void MergeInputSection<ELFT>::splitNonStrings(ArrayRef<uint8_t> Data,
+                                              size_t EntSize) {
   size_t Size = Data.size();
   assert((Size % EntSize) == 0);
-  for (unsigned I = 0, N = Size; I != N; I += EntSize)
-    V.emplace_back(I, Data.slice(I, EntSize));
-  return V;
+  bool IsAlloc = this->Flags & SHF_ALLOC;
+  for (unsigned I = 0, N = Size; I != N; I += EntSize) {
+    Hashes.push_back(hash_value(toStringRef(Data.slice(I, EntSize))));
+    Pieces.emplace_back(I, !IsAlloc);
+  }
 }
 
 template <class ELFT>
 MergeInputSection<ELFT>::MergeInputSection(elf::ObjectFile<ELFT> *F,
-                                           const Elf_Shdr *Header)
-    : SplitInputSection<ELFT>(F, Header, InputSectionBase<ELFT>::Merge) {}
+                                           const Elf_Shdr *Header,
+                                           StringRef Name)
+    : InputSectionBase<ELFT>(F, Header, Name, InputSectionBase<ELFT>::Merge) {}
 
+// This function is called after we obtain a complete list of input sections
+// that need to be linked. This is responsible to split section contents
+// into small chunks for further processing.
+//
+// Note that this function is called from parallel_for_each. This must be
+// thread-safe (i.e. no memory allocation from the pools).
 template <class ELFT> void MergeInputSection<ELFT>::splitIntoPieces() {
-  ArrayRef<uint8_t> Data = this->getSectionData();
-  uintX_t EntSize = this->Header->sh_entsize;
-  if (this->Header->sh_flags & SHF_STRINGS)
-    this->Pieces = splitStrings(Data, EntSize);
+  ArrayRef<uint8_t> Data = this->Data;
+  uintX_t EntSize = this->Entsize;
+  if (this->Flags & SHF_STRINGS)
+    splitStrings(Data, EntSize);
   else
-    this->Pieces = splitNonStrings(Data, EntSize);
+    splitNonStrings(Data, EntSize);
 
-  if (Config->GcSections)
+  if (Config->GcSections && (this->Flags & SHF_ALLOC))
     for (uintX_t Off : LiveOffsets)
       this->getSectionPiece(Off)->Live = true;
 }
 
 template <class ELFT>
-bool MergeInputSection<ELFT>::classof(const InputSectionBase<ELFT> *S) {
-  return S->SectionKind == InputSectionBase<ELFT>::Merge;
+bool MergeInputSection<ELFT>::classof(const InputSectionData *S) {
+  return S->kind() == InputSectionBase<ELFT>::Merge;
 }
 
 // Do binary search to get a section piece at a given input offset.
 template <class ELFT>
-SectionPiece *SplitInputSection<ELFT>::getSectionPiece(uintX_t Offset) {
-  auto *This = static_cast<const SplitInputSection<ELFT> *>(this);
+SectionPiece *MergeInputSection<ELFT>::getSectionPiece(uintX_t Offset) {
+  auto *This = static_cast<const MergeInputSection<ELFT> *>(this);
   return const_cast<SectionPiece *>(This->getSectionPiece(Offset));
 }
 
+template <class It, class T, class Compare>
+static It fastUpperBound(It First, It Last, const T &Value, Compare Comp) {
+  size_t Size = std::distance(First, Last);
+  assert(Size != 0);
+  while (Size != 1) {
+    size_t H = Size / 2;
+    const It MI = First + H;
+    Size -= H;
+    First = Comp(Value, *MI) ? First : First + H;
+  }
+  return Comp(Value, *First) ? First : First + 1;
+}
+
 template <class ELFT>
 const SectionPiece *
-SplitInputSection<ELFT>::getSectionPiece(uintX_t Offset) const {
-  ArrayRef<uint8_t> D = this->getSectionData();
-  StringRef Data((const char *)D.data(), D.size());
-  uintX_t Size = Data.size();
+MergeInputSection<ELFT>::getSectionPiece(uintX_t Offset) const {
+  uintX_t Size = this->Data.size();
   if (Offset >= Size)
-    fatal("entry is past the end of the section");
+    fatal(toString(this) + ": entry is past the end of the section");
 
   // Find the element this offset points to.
-  auto I = std::upper_bound(
+  auto I = fastUpperBound(
       Pieces.begin(), Pieces.end(), Offset,
       [](const uintX_t &A, const SectionPiece &B) { return A < B.InputOff; });
   --I;
@@ -577,84 +799,31 @@ SplitInputSection<ELFT>::getSectionPiece(uintX_t Offset) const {
 // it is not just an addition to a base output offset.
 template <class ELFT>
 typename ELFT::uint MergeInputSection<ELFT>::getOffset(uintX_t Offset) const {
+  // Initialize OffsetMap lazily.
+  std::call_once(InitOffsetMap, [&] {
+    OffsetMap.reserve(Pieces.size());
+    for (const SectionPiece &Piece : Pieces)
+      OffsetMap[Piece.InputOff] = Piece.OutputOff;
+  });
+
+  // Find a string starting at a given offset.
   auto It = OffsetMap.find(Offset);
   if (It != OffsetMap.end())
     return It->second;
 
+  if (!this->Live)
+    return 0;
+
   // If Offset is not at beginning of a section piece, it is not in the map.
   // In that case we need to search from the original section piece vector.
   const SectionPiece &Piece = *this->getSectionPiece(Offset);
-  assert(Piece.Live);
+  if (!Piece.Live)
+    return 0;
+
   uintX_t Addend = Offset - Piece.InputOff;
   return Piece.OutputOff + Addend;
 }
 
-// Create a map from input offsets to output offsets for all section pieces.
-// It is called after finalize().
-template <class ELFT> void  MergeInputSection<ELFT>::finalizePieces() {
-  OffsetMap.grow(this->Pieces.size());
-  for (SectionPiece &Piece : this->Pieces) {
-    if (!Piece.Live)
-      continue;
-    if (Piece.OutputOff == size_t(-1)) {
-      // Offsets of tail-merged strings are computed lazily.
-      auto *OutSec = static_cast<MergeOutputSection<ELFT> *>(this->OutSec);
-      ArrayRef<uint8_t> D = Piece.data();
-      StringRef S((const char *)D.data(), D.size());
-      Piece.OutputOff = OutSec->getOffset(S);
-    }
-    OffsetMap[Piece.InputOff] = Piece.OutputOff;
-  }
-}
-
-template <class ELFT>
-MipsReginfoInputSection<ELFT>::MipsReginfoInputSection(elf::ObjectFile<ELFT> *F,
-                                                       const Elf_Shdr *Hdr)
-    : InputSectionBase<ELFT>(F, Hdr, InputSectionBase<ELFT>::MipsReginfo) {
-  // Initialize this->Reginfo.
-  ArrayRef<uint8_t> D = this->getSectionData();
-  if (D.size() != sizeof(Elf_Mips_RegInfo<ELFT>)) {
-    error("invalid size of .reginfo section");
-    return;
-  }
-  Reginfo = reinterpret_cast<const Elf_Mips_RegInfo<ELFT> *>(D.data());
-}
-
-template <class ELFT>
-bool MipsReginfoInputSection<ELFT>::classof(const InputSectionBase<ELFT> *S) {
-  return S->SectionKind == InputSectionBase<ELFT>::MipsReginfo;
-}
-
-template <class ELFT>
-MipsOptionsInputSection<ELFT>::MipsOptionsInputSection(elf::ObjectFile<ELFT> *F,
-                                                       const Elf_Shdr *Hdr)
-    : InputSectionBase<ELFT>(F, Hdr, InputSectionBase<ELFT>::MipsOptions) {
-  // Find ODK_REGINFO option in the section's content.
-  ArrayRef<uint8_t> D = this->getSectionData();
-  while (!D.empty()) {
-    if (D.size() < sizeof(Elf_Mips_Options<ELFT>)) {
-      error("invalid size of .MIPS.options section");
-      break;
-    }
-    auto *O = reinterpret_cast<const Elf_Mips_Options<ELFT> *>(D.data());
-    if (O->kind == ODK_REGINFO) {
-      Reginfo = &O->getRegInfo();
-      break;
-    }
-    D = D.slice(O->size);
-  }
-}
-
-template <class ELFT>
-bool MipsOptionsInputSection<ELFT>::classof(const InputSectionBase<ELFT> *S) {
-  return S->SectionKind == InputSectionBase<ELFT>::MipsOptions;
-}
-
-template bool elf::isDiscarded<ELF32LE>(InputSectionBase<ELF32LE> *);
-template bool elf::isDiscarded<ELF32BE>(InputSectionBase<ELF32BE> *);
-template bool elf::isDiscarded<ELF64LE>(InputSectionBase<ELF64LE> *);
-template bool elf::isDiscarded<ELF64BE>(InputSectionBase<ELF64BE> *);
-
 template class elf::InputSectionBase<ELF32LE>;
 template class elf::InputSectionBase<ELF32BE>;
 template class elf::InputSectionBase<ELF64LE>;
@@ -665,11 +834,6 @@ template class elf::InputSection<ELF32BE>;
 template class elf::InputSection<ELF64LE>;
 template class elf::InputSection<ELF64BE>;
 
-template class elf::SplitInputSection<ELF32LE>;
-template class elf::SplitInputSection<ELF32BE>;
-template class elf::SplitInputSection<ELF64LE>;
-template class elf::SplitInputSection<ELF64BE>;
-
 template class elf::EhInputSection<ELF32LE>;
 template class elf::EhInputSection<ELF32BE>;
 template class elf::EhInputSection<ELF64LE>;
@@ -680,12 +844,7 @@ template class elf::MergeInputSection<ELF32BE>;
 template class elf::MergeInputSection<ELF64LE>;
 template class elf::MergeInputSection<ELF64BE>;
 
-template class elf::MipsReginfoInputSection<ELF32LE>;
-template class elf::MipsReginfoInputSection<ELF32BE>;
-template class elf::MipsReginfoInputSection<ELF64LE>;
-template class elf::MipsReginfoInputSection<ELF64BE>;
-
-template class elf::MipsOptionsInputSection<ELF32LE>;
-template class elf::MipsOptionsInputSection<ELF32BE>;
-template class elf::MipsOptionsInputSection<ELF64LE>;
-template class elf::MipsOptionsInputSection<ELF64BE>;
+template std::string elf::toString(const InputSectionBase<ELF32LE> *);
+template std::string elf::toString(const InputSectionBase<ELF32BE> *);
+template std::string elf::toString(const InputSectionBase<ELF64LE> *);
+template std::string elf::toString(const InputSectionBase<ELF64BE> *);
diff --git a/ELF/InputSection.h b/ELF/InputSection.h
index 61a89c540c5d..adbc1e1e3829 100644
--- a/ELF/InputSection.h
+++ b/ELF/InputSection.h
@@ -14,25 +14,64 @@
 #include "Relocations.h"
 #include "Thunks.h"
 #include "lld/Core/LLVM.h"
+#include "llvm/ADT/CachedHashString.h"
 #include "llvm/ADT/DenseSet.h"
 #include "llvm/ADT/TinyPtrVector.h"
 #include "llvm/Object/ELF.h"
+#include <mutex>
 
 namespace lld {
 namespace elf {
 
-template <class ELFT> bool isDiscarded(InputSectionBase<ELFT> *S);
-
+class DefinedCommon;
 class SymbolBody;
+struct SectionPiece;
 
-template <class ELFT> class ICF;
 template <class ELFT> class DefinedRegular;
 template <class ELFT> class ObjectFile;
 template <class ELFT> class OutputSection;
-template <class ELFT> class OutputSectionBase;
+class OutputSectionBase;
+
+// We need non-template input section class to store symbol layout
+// in linker script parser structures, where we do not have ELFT
+// template parameter. For each scripted output section symbol we
+// store pointer to preceding InputSectionData object or nullptr,
+// if symbol should be placed at the very beginning of the output
+// section
+class InputSectionData {
+public:
+  enum Kind { Regular, EHFrame, Merge, Synthetic, };
+
+  // The garbage collector sets sections' Live bits.
+  // If GC is disabled, all sections are considered live by default.
+  InputSectionData(Kind SectionKind, StringRef Name, ArrayRef<uint8_t> Data,
+                   bool Live)
+      : SectionKind(SectionKind), Live(Live), Assigned(false), Name(Name),
+        Data(Data) {}
+
+private:
+  unsigned SectionKind : 3;
+
+public:
+  Kind kind() const { return (Kind)SectionKind; }
+
+  unsigned Live : 1;       // for garbage collection
+  unsigned Assigned : 1;   // for linker script
+  uint32_t Alignment;
+  StringRef Name;
+  ArrayRef<uint8_t> Data;
+
+  template <typename T> llvm::ArrayRef<T> getDataAs() const {
+    size_t S = Data.size();
+    assert(S % sizeof(T) == 0);
+    return llvm::makeArrayRef<T>((const T *)Data.data(), S / sizeof(T));
+  }
+
+  std::vector<Relocation> Relocations;
+};
 
 // This corresponds to a section of an input file.
-template <class ELFT> class InputSectionBase {
+template <class ELFT> class InputSectionBase : public InputSectionData {
 protected:
   typedef typename ELFT::Chdr Elf_Chdr;
   typedef typename ELFT::Rel Elf_Rel;
@@ -40,27 +79,46 @@ protected:
   typedef typename ELFT::Shdr Elf_Shdr;
   typedef typename ELFT::Sym Elf_Sym;
   typedef typename ELFT::uint uintX_t;
-  const Elf_Shdr *Header;
 
   // The file this section is from.
   ObjectFile<ELFT> *File;
 
-  // If a section is compressed, this vector has uncompressed section data.
-  SmallVector<char, 0> Uncompressed;
-
 public:
-  enum Kind { Regular, EHFrame, Merge, MipsReginfo, MipsOptions };
-  Kind SectionKind;
-
-  InputSectionBase() : Repl(this) {}
+  // These corresponds to the fields in Elf_Shdr.
+  uintX_t Flags;
+  uintX_t Offset = 0;
+  uintX_t Entsize;
+  uint32_t Type;
+  uint32_t Link;
+  uint32_t Info;
+
+  InputSectionBase()
+      : InputSectionData(Regular, "", ArrayRef<uint8_t>(), false), Repl(this) {
+    NumRelocations = 0;
+    AreRelocsRela = false;
+  }
 
   InputSectionBase(ObjectFile<ELFT> *File, const Elf_Shdr *Header,
+                   StringRef Name, Kind SectionKind);
+  InputSectionBase(ObjectFile<ELFT> *File, uintX_t Flags, uint32_t Type,
+                   uintX_t Entsize, uint32_t Link, uint32_t Info,
+                   uintX_t Addralign, ArrayRef<uint8_t> Data, StringRef Name,
                    Kind SectionKind);
-  OutputSectionBase<ELFT> *OutSec = nullptr;
-  uint32_t Alignment;
-
-  // Used for garbage collection.
-  bool Live;
+  OutputSectionBase *OutSec = nullptr;
+
+  // Relocations that refer to this section.
+  const Elf_Rel *FirstRelocation = nullptr;
+  unsigned NumRelocations : 31;
+  unsigned AreRelocsRela : 1;
+  ArrayRef<Elf_Rel> rels() const {
+    assert(!AreRelocsRela);
+    return llvm::makeArrayRef(FirstRelocation, NumRelocations);
+  }
+  ArrayRef<Elf_Rela> relas() const {
+    assert(AreRelocsRela);
+    return llvm::makeArrayRef(static_cast<const Elf_Rela *>(FirstRelocation),
+                              NumRelocations);
+  }
 
   // This pointer points to the "real" instance of this instance.
   // Usually Repl == this. However, if ICF merges two sections,
@@ -72,140 +130,163 @@ public:
   // Returns the size of this section (even if this is a common or BSS.)
   size_t getSize() const;
 
-  static InputSectionBase<ELFT> Discarded;
-
-  StringRef getSectionName() const;
-  const Elf_Shdr *getSectionHdr() const { return Header; }
   ObjectFile<ELFT> *getFile() const { return File; }
+  llvm::object::ELFFile<ELFT> getObj() const { return File->getObj(); }
   uintX_t getOffset(const DefinedRegular<ELFT> &Sym) const;
-
+  InputSectionBase *getLinkOrderDep() const;
   // Translate an offset in the input section to an offset in the output
   // section.
   uintX_t getOffset(uintX_t Offset) const;
 
-  ArrayRef<uint8_t> getSectionData() const;
-
+  // ELF supports ZLIB-compressed section.
+  // Returns true if the section is compressed.
+  bool isCompressed() const;
   void uncompress();
 
+  // Returns a source location string. Used to construct an error message.
+  std::string getLocation(uintX_t Offset);
+
   void relocate(uint8_t *Buf, uint8_t *BufEnd);
-  std::vector<Relocation<ELFT>> Relocations;
 
-  bool Compressed;
-};
+private:
+  std::pair<ArrayRef<uint8_t>, uint64_t>
+  getElfCompressedData(ArrayRef<uint8_t> Data);
 
-template <class ELFT> InputSectionBase<ELFT> InputSectionBase<ELFT>::Discarded;
+  std::pair<ArrayRef<uint8_t>, uint64_t>
+  getRawCompressedData(ArrayRef<uint8_t> Data);
+};
 
 // SectionPiece represents a piece of splittable section contents.
+// We allocate a lot of these and binary search on them. This means that they
+// have to be as compact as possible, which is why we don't store the size (can
+// be found by looking at the next one) and put the hash in a side table.
 struct SectionPiece {
-  SectionPiece(size_t Off, ArrayRef<uint8_t> Data)
-      : InputOff(Off), Data((const uint8_t *)Data.data()), Size(Data.size()),
-        Live(!Config->GcSections) {}
-
-  ArrayRef<uint8_t> data() { return {Data, Size}; }
-  size_t size() const { return Size; }
+  SectionPiece(size_t Off, bool Live = false)
+      : InputOff(Off), OutputOff(-1), Live(Live || !Config->GcSections) {}
 
   size_t InputOff;
-  size_t OutputOff = -1;
-
-private:
-  // We use bitfields because SplitInputSection is accessed by
-  // std::upper_bound very often.
-  // We want to save bits to make it cache friendly.
-  const uint8_t *Data;
-  uint32_t Size : 31;
-
-public:
-  uint32_t Live : 1;
-};
-
-// Usually sections are copied to the output as atomic chunks of data,
-// but some special types of sections are split into small pieces of data
-// and each piece is copied to a different place in the output.
-// This class represents such special sections.
-template <class ELFT> class SplitInputSection : public InputSectionBase<ELFT> {
-  typedef typename ELFT::Shdr Elf_Shdr;
-  typedef typename ELFT::uint uintX_t;
-
-public:
-  SplitInputSection(ObjectFile<ELFT> *File, const Elf_Shdr *Header,
-                    typename InputSectionBase<ELFT>::Kind SectionKind);
-
-  // Splittable sections are handled as a sequence of data
-  // rather than a single large blob of data.
-  std::vector<SectionPiece> Pieces;
-
-  // Returns the SectionPiece at a given input section offset.
-  SectionPiece *getSectionPiece(uintX_t Offset);
-  const SectionPiece *getSectionPiece(uintX_t Offset) const;
+  ssize_t OutputOff : 8 * sizeof(ssize_t) - 1;
+  size_t Live : 1;
 };
+static_assert(sizeof(SectionPiece) == 2 * sizeof(size_t),
+              "SectionPiece is too big");
 
 // This corresponds to a SHF_MERGE section of an input file.
-template <class ELFT> class MergeInputSection : public SplitInputSection<ELFT> {
+template <class ELFT> class MergeInputSection : public InputSectionBase<ELFT> {
   typedef typename ELFT::uint uintX_t;
   typedef typename ELFT::Sym Elf_Sym;
   typedef typename ELFT::Shdr Elf_Shdr;
 
 public:
-  MergeInputSection(ObjectFile<ELFT> *F, const Elf_Shdr *Header);
-  static bool classof(const InputSectionBase<ELFT> *S);
+  MergeInputSection(ObjectFile<ELFT> *F, const Elf_Shdr *Header,
+                    StringRef Name);
+  static bool classof(const InputSectionData *S);
   void splitIntoPieces();
 
   // Mark the piece at a given offset live. Used by GC.
-  void markLiveAt(uintX_t Offset) { LiveOffsets.insert(Offset); }
+  void markLiveAt(uintX_t Offset) {
+    assert(this->Flags & llvm::ELF::SHF_ALLOC);
+    LiveOffsets.insert(Offset);
+  }
 
   // Translate an offset in the input section to an offset
   // in the output section.
   uintX_t getOffset(uintX_t Offset) const;
 
-  void finalizePieces();
+  // Splittable sections are handled as a sequence of data
+  // rather than a single large blob of data.
+  std::vector<SectionPiece> Pieces;
+
+  // Returns I'th piece's data. This function is very hot when
+  // string merging is enabled, so we want to inline.
+  LLVM_ATTRIBUTE_ALWAYS_INLINE
+  llvm::CachedHashStringRef getData(size_t I) const {
+    size_t Begin = Pieces[I].InputOff;
+    size_t End;
+    if (Pieces.size() - 1 == I)
+      End = this->Data.size();
+    else
+      End = Pieces[I + 1].InputOff;
+
+    StringRef S = {(const char *)(this->Data.data() + Begin), End - Begin};
+    return {S, Hashes[I]};
+  }
+
+  // Returns the SectionPiece at a given input section offset.
+  SectionPiece *getSectionPiece(uintX_t Offset);
+  const SectionPiece *getSectionPiece(uintX_t Offset) const;
 
 private:
-  llvm::DenseMap<uintX_t, uintX_t> OffsetMap;
+  void splitStrings(ArrayRef<uint8_t> A, size_t Size);
+  void splitNonStrings(ArrayRef<uint8_t> A, size_t Size);
+
+  std::vector<uint32_t> Hashes;
+
+  mutable llvm::DenseMap<uintX_t, uintX_t> OffsetMap;
+  mutable std::once_flag InitOffsetMap;
+
   llvm::DenseSet<uintX_t> LiveOffsets;
 };
 
+struct EhSectionPiece : public SectionPiece {
+  EhSectionPiece(size_t Off, InputSectionData *ID, uint32_t Size,
+                 unsigned FirstRelocation)
+      : SectionPiece(Off, false), ID(ID), Size(Size),
+        FirstRelocation(FirstRelocation) {}
+  InputSectionData *ID;
+  uint32_t Size;
+  uint32_t size() const { return Size; }
+
+  ArrayRef<uint8_t> data() { return {ID->Data.data() + this->InputOff, Size}; }
+  unsigned FirstRelocation;
+};
+
 // This corresponds to a .eh_frame section of an input file.
-template <class ELFT> class EhInputSection : public SplitInputSection<ELFT> {
+template <class ELFT> class EhInputSection : public InputSectionBase<ELFT> {
 public:
   typedef typename ELFT::Shdr Elf_Shdr;
   typedef typename ELFT::uint uintX_t;
-  EhInputSection(ObjectFile<ELFT> *F, const Elf_Shdr *Header);
-  static bool classof(const InputSectionBase<ELFT> *S);
+  EhInputSection(ObjectFile<ELFT> *F, const Elf_Shdr *Header, StringRef Name);
+  static bool classof(const InputSectionData *S);
   void split();
+  template <class RelTy> void split(ArrayRef<RelTy> Rels);
 
-  // Translate an offset in the input section to an offset in the output
-  // section.
-  uintX_t getOffset(uintX_t Offset) const;
-
-  // Relocation section that refer to this one.
-  const Elf_Shdr *RelocSection = nullptr;
+  // Splittable sections are handled as a sequence of data
+  // rather than a single large blob of data.
+  std::vector<EhSectionPiece> Pieces;
 };
 
 // This corresponds to a non SHF_MERGE section of an input file.
 template <class ELFT> class InputSection : public InputSectionBase<ELFT> {
-  friend ICF<ELFT>;
   typedef InputSectionBase<ELFT> Base;
   typedef typename ELFT::Shdr Elf_Shdr;
   typedef typename ELFT::Rela Elf_Rela;
   typedef typename ELFT::Rel Elf_Rel;
   typedef typename ELFT::Sym Elf_Sym;
   typedef typename ELFT::uint uintX_t;
+  typedef InputSectionData::Kind Kind;
 
 public:
-  InputSection(ObjectFile<ELFT> *F, const Elf_Shdr *Header);
+  InputSection();
+  InputSection(uintX_t Flags, uint32_t Type, uintX_t Addralign,
+               ArrayRef<uint8_t> Data, StringRef Name,
+               Kind K = InputSectionData::Regular);
+  InputSection(ObjectFile<ELFT> *F, const Elf_Shdr *Header, StringRef Name);
+
+  static InputSection<ELFT> Discarded;
 
   // Write this section to a mmap'ed file, assuming Buf is pointing to
   // beginning of the output section.
   void writeTo(uint8_t *Buf);
 
-  // Relocation sections that refer to this one.
-  llvm::TinyPtrVector<const Elf_Shdr *> RelocSections;
-
   // The offset from beginning of the output sections this section was assigned
   // to. The writer sets a value.
   uint64_t OutSecOff = 0;
 
-  static bool classof(const InputSectionBase<ELFT> *S);
+  // InputSection that is dependent on us (reverse dependency for GC)
+  InputSectionBase<ELFT> *DependentSection = nullptr;
+
+  static bool classof(const InputSectionData *S);
 
   InputSectionBase<ELFT> *getRelocatedSection();
 
@@ -223,46 +304,22 @@ public:
   template <class RelTy>
   void relocateNonAlloc(uint8_t *Buf, llvm::ArrayRef<RelTy> Rels);
 
-private:
-  template <class RelTy>
-  void copyRelocations(uint8_t *Buf, llvm::ArrayRef<RelTy> Rels);
+  // Used by ICF.
+  uint32_t Class[2] = {0, 0};
 
   // Called by ICF to merge two input sections.
   void replace(InputSection<ELFT> *Other);
 
-  // Used by ICF.
-  uint64_t GroupId = 0;
+private:
+  template <class RelTy>
+  void copyRelocations(uint8_t *Buf, llvm::ArrayRef<RelTy> Rels);
 
   llvm::TinyPtrVector<const Thunk<ELFT> *> Thunks;
 };
 
-// MIPS .reginfo section provides information on the registers used by the code
-// in the object file. Linker should collect this information and write a single
-// .reginfo section in the output file. The output section contains a union of
-// used registers masks taken from input .reginfo sections and final value
-// of the `_gp` symbol.  For details: Chapter 4 / "Register Information" at
-// ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
-template <class ELFT>
-class MipsReginfoInputSection : public InputSectionBase<ELFT> {
-  typedef typename ELFT::Shdr Elf_Shdr;
-
-public:
-  MipsReginfoInputSection(ObjectFile<ELFT> *F, const Elf_Shdr *Hdr);
-  static bool classof(const InputSectionBase<ELFT> *S);
-
-  const llvm::object::Elf_Mips_RegInfo<ELFT> *Reginfo = nullptr;
-};
+template <class ELFT> InputSection<ELFT> InputSection<ELFT>::Discarded;
 
-template <class ELFT>
-class MipsOptionsInputSection : public InputSectionBase<ELFT> {
-  typedef typename ELFT::Shdr Elf_Shdr;
-
-public:
-  MipsOptionsInputSection(ObjectFile<ELFT> *F, const Elf_Shdr *Hdr);
-  static bool classof(const InputSectionBase<ELFT> *S);
-
-  const llvm::object::Elf_Mips_RegInfo<ELFT> *Reginfo = nullptr;
-};
+template <class ELFT> std::string toString(const InputSectionBase<ELFT> *);
 
 } // namespace elf
 } // namespace lld
diff --git a/ELF/LTO.cpp b/ELF/LTO.cpp
index 0e8006a3b32a..a3d6a141a202 100644
--- a/ELF/LTO.cpp
+++ b/ELF/LTO.cpp
@@ -9,31 +9,30 @@
 
 #include "LTO.h"
 #include "Config.h"
-#include "Driver.h"
 #include "Error.h"
 #include "InputFiles.h"
 #include "Symbols.h"
-#include "llvm/Analysis/AliasAnalysis.h"
-#include "llvm/Analysis/CGSCCPassManager.h"
-#include "llvm/Analysis/LoopPassManager.h"
-#include "llvm/Analysis/TargetLibraryInfo.h"
-#include "llvm/Analysis/TargetTransformInfo.h"
-#include "llvm/Bitcode/ReaderWriter.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallString.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/Twine.h"
 #include "llvm/CodeGen/CommandFlags.h"
-#include "llvm/CodeGen/ParallelCG.h"
-#include "llvm/IR/AutoUpgrade.h"
-#include "llvm/IR/LegacyPassManager.h"
-#include "llvm/IR/PassManager.h"
-#include "llvm/IR/Verifier.h"
-#include "llvm/LTO/legacy/UpdateCompilerUsed.h"
-#include "llvm/Linker/IRMover.h"
-#include "llvm/Passes/PassBuilder.h"
-#include "llvm/Support/StringSaver.h"
-#include "llvm/Support/TargetRegistry.h"
-#include "llvm/Target/TargetMachine.h"
-#include "llvm/Transforms/IPO.h"
-#include "llvm/Transforms/IPO/PassManagerBuilder.h"
-#include "llvm/Transforms/Utils/ModuleUtils.h"
+#include "llvm/IR/DiagnosticPrinter.h"
+#include "llvm/LTO/Config.h"
+#include "llvm/LTO/LTO.h"
+#include "llvm/Object/SymbolicFile.h"
+#include "llvm/Support/CodeGen.h"
+#include "llvm/Support/ELF.h"
+#include "llvm/Support/Error.h"
+#include "llvm/Support/FileSystem.h"
+#include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Support/raw_ostream.h"
+#include <algorithm>
+#include <cstddef>
+#include <memory>
+#include <string>
+#include <system_error>
+#include <vector>
 
 using namespace llvm;
 using namespace llvm::object;
@@ -51,275 +50,110 @@ static void saveBuffer(StringRef Buffer, const Twine &Path) {
   OS << Buffer;
 }
 
-// This is for use when debugging LTO.
-static void saveBCFile(Module &M, const Twine &Path) {
-  std::error_code EC;
-  raw_fd_ostream OS(Path.str(), EC, sys::fs::OpenFlags::F_None);
-  if (EC)
-    error(EC, "cannot create " + Path);
-  WriteBitcodeToFile(&M, OS, /* ShouldPreserveUseListOrder */ true);
+static void diagnosticHandler(const DiagnosticInfo &DI) {
+  SmallString<128> ErrStorage;
+  raw_svector_ostream OS(ErrStorage);
+  DiagnosticPrinterRawOStream DP(OS);
+  DI.print(DP);
+  warn(ErrStorage);
 }
 
-static void runNewCustomLtoPasses(Module &M, TargetMachine &TM) {
-  PassBuilder PB(&TM);
-
-  AAManager AA;
-
-  // Parse a custom AA pipeline if asked to.
-  if (!PB.parseAAPipeline(AA, Config->LtoAAPipeline)) {
-    error("Unable to parse AA pipeline description: " + Config->LtoAAPipeline);
-    return;
-  }
-
-  LoopAnalysisManager LAM;
-  FunctionAnalysisManager FAM;
-  CGSCCAnalysisManager CGAM;
-  ModuleAnalysisManager MAM;
-
-  // Register the AA manager first so that our version is the one used.
-  FAM.registerPass([&] { return std::move(AA); });
-
-  // Register all the basic analyses with the managers.
-  PB.registerModuleAnalyses(MAM);
-  PB.registerCGSCCAnalyses(CGAM);
-  PB.registerFunctionAnalyses(FAM);
-  PB.registerLoopAnalyses(LAM);
-  PB.crossRegisterProxies(LAM, FAM, CGAM, MAM);
-
-  ModulePassManager MPM;
-  if (!Config->DisableVerify)
-    MPM.addPass(VerifierPass());
+static void checkError(Error E) {
+  handleAllErrors(std::move(E), [&](ErrorInfoBase &EIB) -> Error {
+    error(EIB.message());
+    return Error::success();
+  });
+}
 
-  // Now, add all the passes we've been requested to.
-  if (!PB.parsePassPipeline(MPM, Config->LtoNewPmPasses)) {
-    error("unable to parse pass pipeline description: " +
-          Config->LtoNewPmPasses);
-    return;
-  }
+static std::unique_ptr<lto::LTO> createLTO() {
+  lto::Config Conf;
 
-  if (!Config->DisableVerify)
-    MPM.addPass(VerifierPass());
-  MPM.run(M, MAM);
-}
+  // LLD supports the new relocations.
+  Conf.Options = InitTargetOptionsFromCodeGenFlags();
+  Conf.Options.RelaxELFRelocations = true;
 
-static void runOldLtoPasses(Module &M, TargetMachine &TM) {
-  // Note that the gold plugin has a similar piece of code, so
-  // it is probably better to move this code to a common place.
-  legacy::PassManager LtoPasses;
-  LtoPasses.add(createTargetTransformInfoWrapperPass(TM.getTargetIRAnalysis()));
-  PassManagerBuilder PMB;
-  PMB.LibraryInfo = new TargetLibraryInfoImpl(Triple(TM.getTargetTriple()));
-  PMB.Inliner = createFunctionInliningPass();
-  PMB.VerifyInput = PMB.VerifyOutput = !Config->DisableVerify;
-  PMB.LoopVectorize = true;
-  PMB.SLPVectorize = true;
-  PMB.OptLevel = Config->LtoO;
-  PMB.populateLTOPassManager(LtoPasses);
-  LtoPasses.run(M);
-}
+  Conf.RelocModel = Config->Pic ? Reloc::PIC_ : Reloc::Static;
+  Conf.DisableVerify = Config->DisableVerify;
+  Conf.DiagHandler = diagnosticHandler;
+  Conf.OptLevel = Config->LTOO;
 
-static void runLTOPasses(Module &M, TargetMachine &TM) {
-  if (!Config->LtoNewPmPasses.empty()) {
-    // The user explicitly asked for a set of passes to be run.
-    // This needs the new PM to work as there's no clean way to
-    // pass a set of passes to run in the legacy PM.
-    runNewCustomLtoPasses(M, TM);
-    if (HasError)
-      return;
-  } else {
-    // Run the 'default' set of LTO passes. This code still uses
-    // the legacy PM as the new one is not the default.
-    runOldLtoPasses(M, TM);
-  }
+  // Set up a custom pipeline if we've been asked to.
+  Conf.OptPipeline = Config->LTONewPmPasses;
+  Conf.AAPipeline = Config->LTOAAPipeline;
 
   if (Config->SaveTemps)
-    saveBCFile(M, Config->OutputFile + ".lto.opt.bc");
+    checkError(Conf.addSaveTemps(std::string(Config->OutputFile) + ".",
+                                 /*UseInputModulePath*/ true));
+
+  lto::ThinBackend Backend;
+  if (Config->ThinLTOJobs != -1u)
+    Backend = lto::createInProcessThinBackend(Config->ThinLTOJobs);
+  return llvm::make_unique<lto::LTO>(std::move(Conf), Backend,
+                                     Config->LTOPartitions);
 }
 
-static bool shouldInternalize(const SmallPtrSet<GlobalValue *, 8> &Used,
-                              Symbol *S, GlobalValue *GV) {
-  if (S->IsUsedInRegularObj || Used.count(GV))
-    return false;
-  return !S->includeInDynsym();
-}
+BitcodeCompiler::BitcodeCompiler() : LTOObj(createLTO()) {}
 
-BitcodeCompiler::BitcodeCompiler()
-    : Combined(new Module("ld-temp.o", Driver->Context)) {}
+BitcodeCompiler::~BitcodeCompiler() = default;
 
 static void undefine(Symbol *S) {
-  replaceBody<Undefined>(S, S->body()->getName(), STV_DEFAULT, S->body()->Type,
-                         nullptr);
-}
-
-static void handleUndefinedAsmRefs(const BasicSymbolRef &Sym, GlobalValue *GV,
-                                   StringSet<> &AsmUndefinedRefs) {
-  // GV associated => not an assembly symbol, bail out.
-  if (GV)
-    return;
-
-  // This is an undefined reference to a symbol in asm. We put that in
-  // compiler.used, so that we can preserve it from being dropped from
-  // the output, without necessarily preventing its internalization.
-  SmallString<64> Name;
-  raw_svector_ostream OS(Name);
-  Sym.printName(OS);
-  AsmUndefinedRefs.insert(Name.str());
+  replaceBody<Undefined>(S, S->body()->getName(), /*IsLocal=*/false,
+                         STV_DEFAULT, S->body()->Type, nullptr);
 }
 
 void BitcodeCompiler::add(BitcodeFile &F) {
-  std::unique_ptr<IRObjectFile> Obj = std::move(F.Obj);
-  std::vector<GlobalValue *> Keep;
-  unsigned BodyIndex = 0;
-  ArrayRef<Symbol *> Syms = F.getSymbols();
-
-  Module &M = Obj->getModule();
-  if (M.getDataLayoutStr().empty())
-    fatal("invalid bitcode file: " + F.getName() + " has no datalayout");
-
-  // Discard non-compatible debug infos if necessary.
-  M.materializeMetadata();
-  UpgradeDebugInfo(M);
-
-  // If a symbol appears in @llvm.used, the linker is required
-  // to treat the symbol as there is a reference to the symbol
-  // that it cannot see. Therefore, we can't internalize.
-  SmallPtrSet<GlobalValue *, 8> Used;
-  collectUsedGlobalVariables(M, Used, /* CompilerUsed */ false);
-
-  for (const BasicSymbolRef &Sym : Obj->symbols()) {
-    uint32_t Flags = Sym.getFlags();
-    GlobalValue *GV = Obj->getSymbolGV(Sym.getRawDataRefImpl());
-    if (GV && GV->hasAppendingLinkage())
-      Keep.push_back(GV);
-    if (BitcodeFile::shouldSkip(Flags))
-      continue;
-    Symbol *S = Syms[BodyIndex++];
-    if (Flags & BasicSymbolRef::SF_Undefined) {
-      handleUndefinedAsmRefs(Sym, GV, AsmUndefinedRefs);
-      continue;
-    }
-    auto *B = dyn_cast<DefinedBitcode>(S->body());
-    if (!B || B->file() != &F)
-      continue;
-
-    // We collect the set of symbols we want to internalize here
-    // and change the linkage after the IRMover executed, i.e. after
-    // we imported the symbols and satisfied undefined references
-    // to it. We can't just change linkage here because otherwise
-    // the IRMover will just rename the symbol.
-    if (GV && shouldInternalize(Used, S, GV))
-      InternalizedSyms.insert(GV->getName());
-
-    // At this point we know that either the combined LTO object will provide a
-    // definition of a symbol, or we will internalize it. In either case, we
-    // need to undefine the symbol. In the former case, the real definition
-    // needs to be able to replace the original definition without conflicting.
-    // In the latter case, we need to allow the combined LTO object to provide a
-    // definition with the same name, for example when doing parallel codegen.
-    undefine(S);
-
-    if (!GV)
-      // Module asm symbol.
-      continue;
-
-    switch (GV->getLinkage()) {
-    default:
-      break;
-    case GlobalValue::LinkOnceAnyLinkage:
-      GV->setLinkage(GlobalValue::WeakAnyLinkage);
-      break;
-    case GlobalValue::LinkOnceODRLinkage:
-      GV->setLinkage(GlobalValue::WeakODRLinkage);
-      break;
-    }
-
-    Keep.push_back(GV);
-  }
-
-  IRMover Mover(*Combined);
-  if (Error E = Mover.move(Obj->takeModule(), Keep,
-                           [](GlobalValue &, IRMover::ValueAdder) {})) {
-    handleAllErrors(std::move(E), [&](const ErrorInfoBase &EIB) {
-      fatal("failed to link module " + F.getName() + ": " + EIB.message());
-    });
+  lto::InputFile &Obj = *F.Obj;
+  unsigned SymNum = 0;
+  std::vector<Symbol *> Syms = F.getSymbols();
+  std::vector<lto::SymbolResolution> Resols(Syms.size());
+
+  // Provide a resolution to the LTO API for each symbol.
+  for (const lto::InputFile::Symbol &ObjSym : Obj.symbols()) {
+    Symbol *Sym = Syms[SymNum];
+    lto::SymbolResolution &R = Resols[SymNum];
+    ++SymNum;
+    SymbolBody *B = Sym->body();
+
+    // Ideally we shouldn't check for SF_Undefined but currently IRObjectFile
+    // reports two symbols for module ASM defined. Without this check, lld
+    // flags an undefined in IR with a definition in ASM as prevailing.
+    // Once IRObjectFile is fixed to report only one symbol this hack can
+    // be removed.
+    R.Prevailing =
+        !(ObjSym.getFlags() & object::BasicSymbolRef::SF_Undefined) &&
+        B->File == &F;
+
+    R.VisibleToRegularObj =
+        Sym->IsUsedInRegularObj || (R.Prevailing && Sym->includeInDynsym());
+    if (R.Prevailing)
+      undefine(Sym);
   }
-}
-
-static void internalize(GlobalValue &GV) {
-  assert(!GV.hasLocalLinkage() &&
-         "Trying to internalize a symbol with local linkage!");
-  GV.setLinkage(GlobalValue::InternalLinkage);
-}
-
-std::vector<std::unique_ptr<InputFile>> BitcodeCompiler::runSplitCodegen(
-    const std::function<std::unique_ptr<TargetMachine>()> &TMFactory) {
-  unsigned NumThreads = Config->LtoJobs;
-  OwningData.resize(NumThreads);
-
-  std::list<raw_svector_ostream> OSs;
-  std::vector<raw_pwrite_stream *> OSPtrs;
-  for (SmallString<0> &Obj : OwningData) {
-    OSs.emplace_back(Obj);
-    OSPtrs.push_back(&OSs.back());
-  }
-
-  splitCodeGen(std::move(Combined), OSPtrs, {}, TMFactory);
-
-  std::vector<std::unique_ptr<InputFile>> ObjFiles;
-  for (SmallString<0> &Obj : OwningData)
-    ObjFiles.push_back(createObjectFile(
-        MemoryBufferRef(Obj, "LLD-INTERNAL-combined-lto-object")));
-
-  // If -save-temps is given, we need to save temporary objects to files.
-  // This is for debugging.
-  if (Config->SaveTemps) {
-    if (NumThreads == 1) {
-      saveBuffer(OwningData[0], Config->OutputFile + ".lto.o");
-    } else {
-      for (unsigned I = 0; I < NumThreads; ++I)
-        saveBuffer(OwningData[I], Config->OutputFile + Twine(I) + ".lto.o");
-    }
-  }
-
-  return ObjFiles;
+  checkError(LTOObj->add(std::move(F.Obj), Resols));
 }
 
 // Merge all the bitcode files we have seen, codegen the result
-// and return the resulting ObjectFile.
-std::vector<std::unique_ptr<InputFile>> BitcodeCompiler::compile() {
-  for (const auto &Name : InternalizedSyms) {
-    GlobalValue *GV = Combined->getNamedValue(Name.first());
-    assert(GV);
-    internalize(*GV);
+// and return the resulting ObjectFile(s).
+std::vector<InputFile *> BitcodeCompiler::compile() {
+  std::vector<InputFile *> Ret;
+  unsigned MaxTasks = LTOObj->getMaxTasks();
+  Buff.resize(MaxTasks);
+
+  checkError(LTOObj->run([&](size_t Task) {
+    return llvm::make_unique<lto::NativeObjectStream>(
+        llvm::make_unique<raw_svector_ostream>(Buff[Task]));
+  }));
+
+  for (unsigned I = 0; I != MaxTasks; ++I) {
+    if (Buff[I].empty())
+      continue;
+    if (Config->SaveTemps) {
+      if (MaxTasks == 1)
+        saveBuffer(Buff[I], Config->OutputFile + ".lto.o");
+      else
+        saveBuffer(Buff[I], Config->OutputFile + Twine(I) + ".lto.o");
+    }
+    InputFile *Obj = createObjectFile(MemoryBufferRef(Buff[I], "lto.tmp"));
+    Ret.push_back(Obj);
   }
-
-  std::string TheTriple = Combined->getTargetTriple();
-  std::string Msg;
-  const Target *T = TargetRegistry::lookupTarget(TheTriple, Msg);
-  if (!T)
-    fatal("target not found: " + Msg);
-
-  // LLD supports the new relocations.
-  TargetOptions Options = InitTargetOptionsFromCodeGenFlags();
-  Options.RelaxELFRelocations = true;
-
-  auto CreateTargetMachine = [&]() {
-    return std::unique_ptr<TargetMachine>(T->createTargetMachine(
-        TheTriple, "", "", Options, Config->Pic ? Reloc::PIC_ : Reloc::Static));
-  };
-
-  std::unique_ptr<TargetMachine> TM = CreateTargetMachine();
-
-  // Update llvm.compiler.used so that optimizations won't strip
-  // off AsmUndefinedReferences.
-  updateCompilerUsed(*Combined, *TM, AsmUndefinedRefs);
-
-  if (Config->SaveTemps)
-    saveBCFile(*Combined, Config->OutputFile + ".lto.bc");
-
-  runLTOPasses(*Combined, *TM);
-  if (HasError)
-    return {};
-
-  return runSplitCodegen(CreateTargetMachine);
+  return Ret;
 }
diff --git a/ELF/LTO.h b/ELF/LTO.h
index 81dffb6004b2..b3d734f2d381 100644
--- a/ELF/LTO.h
+++ b/ELF/LTO.h
@@ -23,9 +23,14 @@
 
 #include "lld/Core/LLVM.h"
 #include "llvm/ADT/SmallString.h"
-#include "llvm/ADT/StringSet.h"
-#include "llvm/IR/Module.h"
-#include "llvm/Linker/IRMover.h"
+#include <memory>
+#include <vector>
+
+namespace llvm {
+namespace lto {
+class LTO;
+}
+}
 
 namespace lld {
 namespace elf {
@@ -36,17 +41,14 @@ class InputFile;
 class BitcodeCompiler {
 public:
   BitcodeCompiler();
+  ~BitcodeCompiler();
+
   void add(BitcodeFile &F);
-  std::vector<std::unique_ptr<InputFile>> compile();
+  std::vector<InputFile *> compile();
 
 private:
-  std::vector<std::unique_ptr<InputFile>> runSplitCodegen(
-      const std::function<std::unique_ptr<llvm::TargetMachine>()> &TMFactory);
-
-  std::unique_ptr<llvm::Module> Combined;
-  std::vector<SmallString<0>> OwningData;
-  llvm::StringSet<> InternalizedSyms;
-  llvm::StringSet<> AsmUndefinedRefs;
+  std::unique_ptr<llvm::lto::LTO> LTOObj;
+  std::vector<SmallString<0>> Buff;
 };
 }
 }
diff --git a/ELF/LinkerScript.cpp b/ELF/LinkerScript.cpp
index 61abdc185e11..5057b57a4a54 100644
--- a/ELF/LinkerScript.cpp
+++ b/ELF/LinkerScript.cpp
@@ -8,8 +8,6 @@
 //===----------------------------------------------------------------------===//
 //
 // This file contains the parser/evaluator of the linker script.
-// It does not construct an AST but consume linker script directives directly.
-// Results are written to Driver or Config object.
 //
 //===----------------------------------------------------------------------===//
 
@@ -17,311 +15,971 @@
 #include "Config.h"
 #include "Driver.h"
 #include "InputSection.h"
+#include "Memory.h"
 #include "OutputSections.h"
 #include "ScriptParser.h"
 #include "Strings.h"
-#include "Symbols.h"
 #include "SymbolTable.h"
+#include "Symbols.h"
+#include "SyntheticSections.h"
 #include "Target.h"
+#include "Writer.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallString.h"
+#include "llvm/ADT/StringRef.h"
 #include "llvm/ADT/StringSwitch.h"
+#include "llvm/Support/Casting.h"
 #include "llvm/Support/ELF.h"
+#include "llvm/Support/Endian.h"
+#include "llvm/Support/ErrorHandling.h"
 #include "llvm/Support/FileSystem.h"
-#include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Support/MathExtras.h"
 #include "llvm/Support/Path.h"
-#include "llvm/Support/StringSaver.h"
+#include <algorithm>
+#include <cassert>
+#include <cstddef>
+#include <cstdint>
+#include <iterator>
+#include <limits>
+#include <memory>
+#include <string>
+#include <tuple>
+#include <vector>
 
 using namespace llvm;
 using namespace llvm::ELF;
 using namespace llvm::object;
+using namespace llvm::support::endian;
 using namespace lld;
 using namespace lld::elf;
 
+LinkerScriptBase *elf::ScriptBase;
 ScriptConfiguration *elf::ScriptConfig;
 
-// This is an operator-precedence parser to parse and evaluate
-// a linker script expression. For each linker script arithmetic
-// expression (e.g. ". = . + 0x1000"), a new instance of ExprParser
-// is created and ran.
-namespace {
-class ExprParser : public ScriptParserBase {
-public:
-  ExprParser(std::vector<StringRef> &Tokens, uint64_t Dot)
-      : ScriptParserBase(Tokens), Dot(Dot) {}
+template <class ELFT> static void addRegular(SymbolAssignment *Cmd) {
+  uint8_t Visibility = Cmd->Hidden ? STV_HIDDEN : STV_DEFAULT;
+  Symbol *Sym = Symtab<ELFT>::X->addRegular(Cmd->Name, Visibility, STT_NOTYPE,
+                                            0, 0, STB_GLOBAL, nullptr, nullptr);
+  Cmd->Sym = Sym->body();
 
-  uint64_t run();
+  // If we have no SECTIONS then we don't have '.' and don't call
+  // assignAddresses(). We calculate symbol value immediately in this case.
+  if (!ScriptConfig->HasSections)
+    cast<