diff --git a/llvm/include/llvm/LTO/legacy/LTOCodeGenerator.h b/llvm/include/llvm/LTO/legacy/LTOCodeGenerator.h
--- a/llvm/include/llvm/LTO/legacy/LTOCodeGenerator.h
+++ b/llvm/include/llvm/LTO/legacy/LTOCodeGenerator.h
@@ -213,6 +213,15 @@
   bool determineTarget();
   std::unique_ptr<TargetMachine> createTargetMachine();
 
+  // Checks to see if the llvm backend integrated assembler is available.
+  bool hasIntegratedAssembler();
+
+  // Sets up the LTO configuration to run the system assembler.
+  void setupForSystemAssembler();
+
+  // Runs the system assembler to generate object file.
+  bool runSystemAssembler(SmallString<128> &Name);
+
   void emitError(const std::string &ErrMsg);
   void emitWarning(const std::string &ErrMsg);
 
diff --git a/llvm/lib/LTO/LTOCodeGenerator.cpp b/llvm/lib/LTO/LTOCodeGenerator.cpp
--- a/llvm/lib/LTO/LTOCodeGenerator.cpp
+++ b/llvm/lib/LTO/LTOCodeGenerator.cpp
@@ -51,6 +51,7 @@
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/Host.h"
 #include "llvm/Support/MemoryBuffer.h"
+#include "llvm/Support/Process.h"
 #include "llvm/Support/Signals.h"
 #include "llvm/Support/TargetSelect.h"
 #include "llvm/Support/ToolOutputFile.h"
@@ -64,6 +65,13 @@
 #include "llvm/Transforms/ObjCARC.h"
 #include "llvm/Transforms/Utils/ModuleUtils.h"
 #include <system_error>
+#if defined(HAVE_UNISTD_H)
+#include <unistd.h>
+#define GETPID getpid()
+#else
+#define GETPID 0
+#endif
+
 using namespace llvm;
 
 const char* LTOCodeGenerator::getVersionString() {
@@ -114,6 +122,15 @@
     "lto-stats-file",
     cl::desc("Save statistics to the specified file"),
     cl::Hidden);
+
+cl::opt<bool> SaveTemps(
+    "lto-save-temps", cl::init(false),
+    cl::desc("Save temporary LTO files in the current working directory."));
+
+cl::opt<std::string> SystemAssemblerPath(
+    "lto-system-assembler",
+    cl::desc("Absolute path to the system assembler, picked up on AIX only"),
+    cl::value_desc("path"));
 }
 
 LTOCodeGenerator::LTOCodeGenerator(LLVMContext &Context)
@@ -237,7 +254,75 @@
   return true;
 }
 
+bool LTOCodeGenerator::hasIntegratedAssembler() {
+  const auto &Triple = TargetMach->getTargetTriple();
+  return !Triple.isOSAIX();
+}
+
+void LTOCodeGenerator::setupForSystemAssembler() {
+  setFileType(CGFT_AssemblyFile);
+}
+
+bool LTOCodeGenerator::runSystemAssembler(SmallString<128> &Name) {
+  assert(!hasIntegratedAssembler() &&
+         "Runing system assembler when integrated assembler is available!");
+
+  if (llvm::SaveTemps)
+    llvm::sys::fs::copy_file(Name, "ld-temp." + llvm::Twine(getpid()) + ".s");
+
+  // Set the system assembler path.
+  std::string AssemblerPath(llvm::SystemAssemblerPath.empty()
+                                ? "/usr/bin/as"
+                                : llvm::SystemAssemblerPath.c_str());
+
+  // Prepare inputs for the assember.
+  const auto &Triple = TargetMach->getTargetTriple();
+  const char *Arch = Triple.isArch64Bit() ? "-a64" : "-a32";
+  std::string ObjectFileName(Name);
+  ObjectFileName[ObjectFileName.size() - 1] = 'o';
+  SmallVector<StringRef, 8> Args = {
+      "/bin/env",     "LDR_CNTRL=MAXDATA32=0x80000000@${LDR_CNTRL}",
+      AssemblerPath,  Arch,
+      "-many",        "-o",
+      ObjectFileName, Name};
+
+  // Invoke the assembler.
+  int RC = sys::ExecuteAndWait(Args[0], Args);
+
+  // Handle errors.
+  if (RC < -1) {
+    emitError("LTO assembler exited abnormally");
+    return false;
+  }
+
+  if (RC < 0) {
+    emitError("Unable to invoke LTO assembler");
+    return false;
+  }
+
+  if (RC > 0) {
+    emitError("LTO assembler invocation returned non-zero");
+    return false;
+  }
+
+  // Cleanup.
+  remove(Name.c_str());
+
+  if (llvm::SaveTemps)
+    llvm::sys::fs::copy_file(ObjectFileName,
+                             "ld-temp." + llvm::Twine(getpid()) + ".postlto.o");
+
+  // Fix the output file name.
+  Name = ObjectFileName;
+
+  return true;
+}
+
 bool LTOCodeGenerator::compileOptimizedToFile(const char **Name) {
+  if (!hasIntegratedAssembler()) {
+    setupForSystemAssembler();
+  }
+
   // make unique temp output file to put generated code
   SmallString<128> Filename;
 
@@ -268,6 +353,10 @@
   else if (AreStatisticsEnabled())
     PrintStatistics();
 
+  if (!hasIntegratedAssembler())
+    if (!runSystemAssembler(Filename))
+      return false;
+
   NativeObjectPath = Filename.c_str();
   *Name = NativeObjectPath.c_str();
   return true;