Index: llvm/trunk/include/llvm/LTO/Config.h
===================================================================
--- llvm/trunk/include/llvm/LTO/Config.h
+++ llvm/trunk/include/llvm/LTO/Config.h
@@ -52,6 +52,9 @@
   unsigned OptLevel = 2;
   bool DisableVerify = false;
 
+  /// Disable entirely the optimizer, including importing for ThinLTO
+  bool CodeGenOnly = false;
+
   /// Setting this field will replace target triples in input files with this
   /// triple.
   std::string OverrideTriple;
Index: llvm/trunk/lib/LTO/LTO.cpp
===================================================================
--- llvm/trunk/lib/LTO/LTO.cpp
+++ llvm/trunk/lib/LTO/LTO.cpp
@@ -365,27 +365,29 @@
       !Conf.PreOptModuleHook(0, *RegularLTO.CombinedModule))
     return Error();
 
-  for (const auto &R : GlobalResolutions) {
-    if (R.second.IRName.empty())
-      continue;
-    if (R.second.Partition != 0 &&
-        R.second.Partition != GlobalResolution::External)
-      continue;
+  if (!Conf.CodeGenOnly) {
+    for (const auto &R : GlobalResolutions) {
+      if (R.second.IRName.empty())
+        continue;
+      if (R.second.Partition != 0 &&
+          R.second.Partition != GlobalResolution::External)
+        continue;
+
+      GlobalValue *GV =
+          RegularLTO.CombinedModule->getNamedValue(R.second.IRName);
+      // Ignore symbols defined in other partitions.
+      if (!GV || GV->hasLocalLinkage())
+        continue;
+      GV->setUnnamedAddr(R.second.UnnamedAddr ? GlobalValue::UnnamedAddr::Global
+                                              : GlobalValue::UnnamedAddr::None);
+      if (R.second.Partition == 0)
+        GV->setLinkage(GlobalValue::InternalLinkage);
+    }
 
-    GlobalValue *GV = RegularLTO.CombinedModule->getNamedValue(R.second.IRName);
-    // Ignore symbols defined in other partitions.
-    if (!GV || GV->hasLocalLinkage())
-      continue;
-    GV->setUnnamedAddr(R.second.UnnamedAddr ? GlobalValue::UnnamedAddr::Global
-                                            : GlobalValue::UnnamedAddr::None);
-    if (R.second.Partition == 0)
-      GV->setLinkage(GlobalValue::InternalLinkage);
+    if (Conf.PostInternalizeModuleHook &&
+        !Conf.PostInternalizeModuleHook(0, *RegularLTO.CombinedModule))
+      return Error();
   }
-
-  if (Conf.PostInternalizeModuleHook &&
-      !Conf.PostInternalizeModuleHook(0, *RegularLTO.CombinedModule))
-    return Error();
-
   return backend(Conf, AddOutput, RegularLTO.ParallelCodeGenParallelismLevel,
                  std::move(RegularLTO.CombinedModule));
 }
Index: llvm/trunk/lib/LTO/LTOBackend.cpp
===================================================================
--- llvm/trunk/lib/LTO/LTOBackend.cpp
+++ llvm/trunk/lib/LTO/LTOBackend.cpp
@@ -224,8 +224,9 @@
   std::unique_ptr<TargetMachine> TM =
       createTargetMachine(C, M->getTargetTriple(), *TOrErr);
 
-  if (!opt(C, TM.get(), 0, *M, /*IsThinLto=*/false))
-    return Error();
+  if (!C.CodeGenOnly)
+    if (!opt(C, TM.get(), 0, *M, /*IsThinLto=*/false))
+      return Error();
 
   if (ParallelCodeGenParallelismLevel == 1)
     codegen(C, TM.get(), AddOutput, 0, *M);
@@ -247,6 +248,11 @@
   std::unique_ptr<TargetMachine> TM =
       createTargetMachine(Conf, Mod.getTargetTriple(), *TOrErr);
 
+  if (Conf.CodeGenOnly) {
+    codegen(Conf, TM.get(), AddOutput, Task, Mod);
+    return Error();
+  }
+
   if (Conf.PreOptModuleHook && !Conf.PreOptModuleHook(Task, Mod))
     return Error();