diff --git a/llvm/include/llvm/LTO/LTOBackend.h b/llvm/include/llvm/LTO/LTOBackend.h
--- a/llvm/include/llvm/LTO/LTOBackend.h
+++ b/llvm/include/llvm/LTO/LTOBackend.h
@@ -33,6 +33,12 @@
 
 namespace lto {
 
+/// Runs middle-end LTO optimizations on \p Mod.
+bool opt(const Config &Conf, TargetMachine *TM, unsigned Task, Module &Mod,
+         bool IsThinLTO, ModuleSummaryIndex *ExportSummary,
+         const ModuleSummaryIndex *ImportSummary,
+         const std::vector<uint8_t> &CmdArgs);
+
 /// Runs a regular LTO backend. The regular LTO backend can also act as the
 /// regular LTO phase of ThinLTO, which may need to access the combined index.
 Error backend(const Config &C, AddStreamFn AddStream,
diff --git a/llvm/lib/LTO/LTOBackend.cpp b/llvm/lib/LTO/LTOBackend.cpp
--- a/llvm/lib/LTO/LTOBackend.cpp
+++ b/llvm/lib/LTO/LTOBackend.cpp
@@ -360,39 +360,6 @@
   passes.run(Mod);
 }
 
-bool opt(const Config &Conf, TargetMachine *TM, unsigned Task, Module &Mod,
-         bool IsThinLTO, ModuleSummaryIndex *ExportSummary,
-         const ModuleSummaryIndex *ImportSummary,
-         const std::vector<uint8_t> &CmdArgs) {
-  if (EmbedBitcode == LTOBitcodeEmbedding::EmbedPostMergePreOptimized) {
-    // FIXME: the motivation for capturing post-merge bitcode and command line
-    // is replicating the compilation environment from bitcode, without needing
-    // to understand the dependencies (the functions to be imported). This
-    // assumes a clang - based invocation, case in which we have the command
-    // line.
-    // It's not very clear how the above motivation would map in the
-    // linker-based case, so we currently don't plumb the command line args in
-    // that case.
-    if (CmdArgs.empty())
-      LLVM_DEBUG(
-          dbgs() << "Post-(Thin)LTO merge bitcode embedding was requested, but "
-                    "command line arguments are not available");
-    llvm::EmbedBitcodeInModule(Mod, llvm::MemoryBufferRef(),
-                               /*EmbedBitcode*/ true, /*EmbedCmdline*/ true,
-                               /*Cmdline*/ CmdArgs);
-  }
-  // FIXME: Plumb the combined index into the new pass manager.
-  if (!Conf.OptPipeline.empty())
-    runNewPMCustomPasses(Conf, Mod, TM, Conf.OptPipeline, Conf.AAPipeline,
-                         Conf.DisableVerify);
-  else if (Conf.UseNewPM)
-    runNewPMPasses(Conf, Mod, TM, Conf.OptLevel, IsThinLTO, ExportSummary,
-                   ImportSummary);
-  else
-    runOldPMPasses(Conf, Mod, TM, IsThinLTO, ExportSummary, ImportSummary);
-  return !Conf.PostOptModuleHook || Conf.PostOptModuleHook(Task, Mod);
-}
-
 void codegen(const Config &Conf, TargetMachine *TM, AddStreamFn AddStream,
              unsigned Task, Module &Mod,
              const ModuleSummaryIndex &CombinedIndex) {
@@ -516,6 +483,39 @@
   return Error::success();
 }
 
+bool lto::opt(const Config &Conf, TargetMachine *TM, unsigned Task, Module &Mod,
+              bool IsThinLTO, ModuleSummaryIndex *ExportSummary,
+              const ModuleSummaryIndex *ImportSummary,
+              const std::vector<uint8_t> &CmdArgs) {
+  if (EmbedBitcode == LTOBitcodeEmbedding::EmbedPostMergePreOptimized) {
+    // FIXME: the motivation for capturing post-merge bitcode and command line
+    // is replicating the compilation environment from bitcode, without needing
+    // to understand the dependencies (the functions to be imported). This
+    // assumes a clang - based invocation, case in which we have the command
+    // line.
+    // It's not very clear how the above motivation would map in the
+    // linker-based case, so we currently don't plumb the command line args in
+    // that case.
+    if (CmdArgs.empty())
+      LLVM_DEBUG(
+          dbgs() << "Post-(Thin)LTO merge bitcode embedding was requested, but "
+                    "command line arguments are not available");
+    llvm::EmbedBitcodeInModule(Mod, llvm::MemoryBufferRef(),
+                               /*EmbedBitcode*/ true, /*EmbedCmdline*/ true,
+                               /*Cmdline*/ CmdArgs);
+  }
+  // FIXME: Plumb the combined index into the new pass manager.
+  if (!Conf.OptPipeline.empty())
+    runNewPMCustomPasses(Conf, Mod, TM, Conf.OptPipeline, Conf.AAPipeline,
+                         Conf.DisableVerify);
+  else if (Conf.UseNewPM)
+    runNewPMPasses(Conf, Mod, TM, Conf.OptLevel, IsThinLTO, ExportSummary,
+                   ImportSummary);
+  else
+    runOldPMPasses(Conf, Mod, TM, IsThinLTO, ExportSummary, ImportSummary);
+  return !Conf.PostOptModuleHook || Conf.PostOptModuleHook(Task, Mod);
+}
+
 Error lto::backend(const Config &C, AddStreamFn AddStream,
                    unsigned ParallelCodeGenParallelismLevel,
                    std::unique_ptr<Module> Mod,