Index: llvm/trunk/include/llvm/LTO/Config.h
===================================================================
--- llvm/trunk/include/llvm/LTO/Config.h
+++ llvm/trunk/include/llvm/LTO/Config.h
@@ -73,6 +73,12 @@
   /// Sample PGO profile path.
   std::string SampleProfile;
 
+  /// The directory to store .dwo files.
+  std::string DwoDir;
+
+  /// The objcopy binary used to extract dwo files.
+  std::string Objcopy;
+
   /// Optimization remarks file path.
   std::string RemarksFilename = "";
 
Index: llvm/trunk/lib/LTO/LTO.cpp
===================================================================
--- llvm/trunk/lib/LTO/LTO.cpp
+++ llvm/trunk/lib/LTO/LTO.cpp
@@ -136,6 +136,7 @@
   AddString(Conf.AAPipeline);
   AddString(Conf.OverrideTriple);
   AddString(Conf.DefaultTriple);
+  AddString(Conf.DwoDir);
 
   // Include the hash for the current module
   auto ModHash = Index.getModuleHash(ModuleID);
Index: llvm/trunk/lib/LTO/LTOBackend.cpp
===================================================================
--- llvm/trunk/lib/LTO/LTOBackend.cpp
+++ llvm/trunk/lib/LTO/LTOBackend.cpp
@@ -30,6 +30,10 @@
 #include "llvm/Passes/PassBuilder.h"
 #include "llvm/Support/Error.h"
 #include "llvm/Support/FileSystem.h"
+#include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Support/Path.h"
+#include "llvm/Support/Program.h"
+#include "llvm/Support/raw_ostream.h"
 #include "llvm/Support/TargetRegistry.h"
 #include "llvm/Support/ThreadPool.h"
 #include "llvm/Target/TargetMachine.h"
@@ -279,11 +283,74 @@
   return !Conf.PostOptModuleHook || Conf.PostOptModuleHook(Task, Mod);
 }
 
+void codegenWithSplitDwarf(Config &Conf, TargetMachine *TM,
+                           AddStreamFn AddStream, unsigned Task, Module &Mod) {
+  SmallString<128> TempFile;
+  int FD = -1;
+  if (auto EC =
+      sys::fs::createTemporaryFile("lto-llvm-fission", "o", FD, TempFile))
+    report_fatal_error("Could not create temporary file " +
+        TempFile.str() + ": " + EC.message());
+  llvm::raw_fd_ostream OS(FD, true);
+  SmallString<1024> DwarfFile(Conf.DwoDir);
+  std::string DwoName = sys::path::filename(Mod.getModuleIdentifier()).str() +
+      "-" + std::to_string(Task) + "-";
+  size_t index = TempFile.str().rfind("lto-llvm-fission");
+  StringRef TempID = TempFile.str().substr(index + 17, 6);
+  DwoName += TempID.str() + ".dwo";
+  sys::path::append(DwarfFile, DwoName);
+  TM->Options.MCOptions.SplitDwarfFile = DwarfFile.str().str();
+
+  legacy::PassManager CodeGenPasses;
+  if (TM->addPassesToEmitFile(CodeGenPasses, OS, Conf.CGFileType))
+    report_fatal_error("Failed to setup codegen");
+  CodeGenPasses.run(Mod);
+
+  if (auto EC = llvm::sys::fs::create_directories(Conf.DwoDir))
+    report_fatal_error("Failed to create directory " +
+		       Conf.DwoDir + ": " + EC.message());
+
+  SmallVector<const char*, 5> ExtractArgs, StripArgs;
+  ExtractArgs.push_back(Conf.Objcopy.c_str());
+  ExtractArgs.push_back("--extract-dwo");
+  ExtractArgs.push_back(TempFile.c_str());
+  ExtractArgs.push_back(TM->Options.MCOptions.SplitDwarfFile.c_str());
+  ExtractArgs.push_back(nullptr);
+  StripArgs.push_back(Conf.Objcopy.c_str());
+  StripArgs.push_back("--strip-dwo");
+  StripArgs.push_back(TempFile.c_str());
+  StripArgs.push_back(nullptr);
+
+  if (auto Ret = sys::ExecuteAndWait(Conf.Objcopy, ExtractArgs.data())) {
+    report_fatal_error("Failed to extract dwo from " + TempFile.str() +
+        ". Exit code " + std::to_string(Ret));
+  }
+  if (auto Ret = sys::ExecuteAndWait(Conf.Objcopy, StripArgs.data())) {
+    report_fatal_error("Failed to strip dwo from " + TempFile.str() +
+        ". Exit code " + std::to_string(Ret));
+  }
+
+  auto Stream = AddStream(Task);
+  auto Buffer = MemoryBuffer::getFile(TempFile);
+  if (auto EC = Buffer.getError())
+    report_fatal_error("Failed to load file " +
+                       TempFile.str() + ": " + EC.message());
+  *Stream->OS << Buffer.get()->getBuffer();
+  if (auto EC = sys::fs::remove(TempFile))
+    report_fatal_error("Failed to delete file " +
+                       TempFile.str() + ": " + EC.message());
+}
+
 void codegen(Config &Conf, TargetMachine *TM, AddStreamFn AddStream,
              unsigned Task, Module &Mod) {
   if (Conf.PreCodeGenModuleHook && !Conf.PreCodeGenModuleHook(Task, Mod))
     return;
 
+  if (!Conf.DwoDir.empty()) {
+    codegenWithSplitDwarf(Conf, TM, AddStream, Task, Mod);
+    return;
+  }
+
   auto Stream = AddStream(Task);
   legacy::PassManager CodeGenPasses;
   if (TM->addPassesToEmitFile(CodeGenPasses, *Stream->OS, Conf.CGFileType))
Index: llvm/trunk/test/lit.cfg.py
===================================================================
--- llvm/trunk/test/lit.cfg.py
+++ llvm/trunk/test/lit.cfg.py
@@ -134,6 +134,7 @@
     ToolSubst('%ocamlc', ocamlc_command, unresolved='ignore'),
     ToolSubst('%ocamlopt', ocamlopt_command, unresolved='ignore'),
     ToolSubst('%opt-viewer', opt_viewer_cmd),
+    ToolSubst('%llvm-objcopy', FindTool('llvm-objcopy')),
 ]
 
 # FIXME: Why do we have both `lli` and `%lli` that do slightly different things?
Index: llvm/trunk/test/tools/gold/X86/split-dwarf.ll
===================================================================
--- llvm/trunk/test/tools/gold/X86/split-dwarf.ll
+++ llvm/trunk/test/tools/gold/X86/split-dwarf.ll
@@ -0,0 +1,63 @@
+; RUN: rm -rf %t && mkdir -p %t
+; RUN: opt -module-summary %s -o %t/split-dwarf.o
+; RUN: %gold -plugin %llvmshlibdir/LLVMgold%shlibext  \
+; RUN:    -m elf_x86_64 \
+; RUN:    --plugin-opt=thinlto \
+; RUN:    --plugin-opt=objcopy=%llvm-objcopy \
+; RUN:    --plugin-opt=dwo_dir=%t/dwo_dir \
+; RUN:    %t/split-dwarf.o --shared -o %t/split-dwarf
+
+; RUN: llvm-dwarfdump -debug-info %t/split-dwarf | FileCheck %s
+; CHECK: DW_AT_GNU_dwo_name{{.*}}dwo_dir/split-dwarf.{{.*}}
+; CHECK-NOT: DW_TAG_subprogram
+; RUN: llvm-dwarfdump -debug-info %t/dwo_dir/split-dwarf.* | FileCheck --check-prefix DWOCHECK %s
+; DWOCHECK: DW_AT_GNU_dwo_name{{.*}}dwo_dir/split-dwarf.o{{.*}}
+; DWOCHECK: DW_AT_name{{.*}}split-dwarf.c
+; DWOCHECK: DW_TAG_subprogram
+
+; RUN:rm -rf %t/dwo_dir
+; RUN: opt  %s -o %t/split-dwarf.o
+; RUN: %gold -plugin %llvmshlibdir/LLVMgold%shlibext  \
+; RUN:    -m elf_x86_64 \
+; RUN:    --plugin-opt=thinlto \
+; RUN:    --plugin-opt=objcopy=%llvm-objcopy \
+; RUN:    --plugin-opt=dwo_dir=%t/dwo_dir \
+; RUN:    %t/split-dwarf.o --shared -o %t/split-dwarf
+
+; RUN: llvm-dwarfdump -debug-info %t/split-dwarf | FileCheck --check-prefix LTOCHECK %s
+; LTOCHECK: DW_AT_GNU_dwo_name{{.*}}dwo_dir/ld-temp.{{.*}}
+; LTOCHECK-NOT: DW_TAG_subprogram
+; RUN: llvm-dwarfdump -debug-info %t/dwo_dir/ld-temp.* | FileCheck --check-prefix LTODWOCHECK %s
+; LTODWOCHECK: DW_AT_GNU_dwo_name{{.*}}dwo_dir/ld-temp.o{{.*}}
+; LTODWOCHECK: DW_AT_name{{.*}}split-dwarf.c
+; LTODWOCHECK: DW_TAG_subprogram
+
+; ModuleID = 'split-dwarf.c'
+source_filename = "split-dwarf.c"
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; Function Attrs: noinline nounwind optnone uwtable
+define dso_local i32 @split_dwarf() #0 !dbg !7 {
+entry:
+  ret i32 0, !dbg !11
+}
+
+attributes #0 = { noinline nounwind optnone uwtable "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-infs-fp-math"="false" "no-jump-tables"="false" "no-nans-fp-math"="false" "no-signed-zeros-fp-math"="false" "no-trapping-math"="false" "stack-protector-buffer-size"="8" "target-cpu"="x86-64" "target-features"="+fxsr,+mmx,+sse,+sse2,+x87" "unsafe-fp-math"="false" "use-soft-float"="false" }
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang version 7.0.0 (https://github.com/llvm-mirror/clang.git b641d31365414ba3ea0305fdaa80369a9efb6bd9) (https://github.com/llvm-mirror/llvm.git 6165a776d1a8bb181be93f2dc97088f7a1abc405)", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "split-dwarf.c", directory: "/usr/local/google/home/yunlian/dwp/build/bin")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang version 7.0.0 (https://github.com/llvm-mirror/clang.git b641d31365414ba3ea0305fdaa80369a9efb6bd9) (https://github.com/llvm-mirror/llvm.git 6165a776d1a8bb181be93f2dc97088f7a1abc405)"}
+!7 = distinct !DISubprogram(name: "split_dwarf", scope: !1, file: !1, line: 1, type: !8, isLocal: false, isDefinition: true, scopeLine: 1, isOptimized: false, unit: !0, variables: !2)
+!8 = !DISubroutineType(types: !9)
+!9 = !{!10}
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = !DILocation(line: 2, column: 2, scope: !7)
Index: llvm/trunk/tools/gold/gold-plugin.cpp
===================================================================
--- llvm/trunk/tools/gold/gold-plugin.cpp
+++ llvm/trunk/tools/gold/gold-plugin.cpp
@@ -199,6 +199,10 @@
   static bool new_pass_manager = false;
   // Debug new pass manager
   static bool debug_pass_manager = false;
+  // Objcopy for debug fission.
+  static std::string objcopy;
+  // Directory to store the .dwo files.
+  static std::string dwo_dir;
 
   static void process_plugin_option(const char *opt_)
   {
@@ -262,6 +266,10 @@
       new_pass_manager = true;
     } else if (opt == "debug-pass-manager") {
       debug_pass_manager = true;
+    } else if (opt.startswith("objcopy=")) {
+      objcopy = opt.substr(strlen("objcopy="));
+    } else if (opt.startswith("dwo_dir=")) {
+      dwo_dir = opt.substr(strlen("dwo_dir="));
     } else {
       // Save this option to pass to the code generator.
       // ParseCommandLineOptions() expects argv[0] to be program name. Lazily
@@ -870,6 +878,10 @@
   if (!options::sample_profile.empty())
     Conf.SampleProfile = options::sample_profile;
 
+  Conf.DwoDir = options::dwo_dir;
+
+  Conf.Objcopy = options::objcopy;
+
   // Use new pass manager if set in driver
   Conf.UseNewPM = options::new_pass_manager;
   // Debug new pass manager if requested