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
@@ -358,10 +358,10 @@
   passes.run(Mod);
 }
 
-static bool opt(const Config &Conf, TargetMachine *TM, unsigned Task,
-                Module &Mod, bool IsThinLTO, ModuleSummaryIndex *ExportSummary,
-                const ModuleSummaryIndex *ImportSummary,
-                const std::vector<uint8_t> &CmdArgs) {
+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