[ThinLTO] Helper for performing renaming/promotion on a module

Creates a module and performs necessary renaming/promotion of locals
that may be exported to another module.

Split out of D15024.

llvm-svn: 254802
diff --git a/llvm/lib/Linker/LinkModules.cpp b/llvm/lib/Linker/LinkModules.cpp
index 88b8e44..627137b 100644
--- a/llvm/lib/Linker/LinkModules.cpp
+++ b/llvm/lib/Linker/LinkModules.cpp
@@ -2056,6 +2056,18 @@
   return L.linkInModule(Src, Flags);
 }
 
+std::unique_ptr<Module>
+llvm::renameModuleForThinLTO(std::unique_ptr<Module> &M,
+                             const FunctionInfoIndex *Index,
+                             DiagnosticHandlerFunction DiagnosticHandler) {
+  std::unique_ptr<llvm::Module> RenamedModule(
+      new llvm::Module(M->getModuleIdentifier(), M->getContext()));
+  Linker L(*RenamedModule.get(), DiagnosticHandler);
+  if (L.linkInModule(*M.get(), llvm::Linker::Flags::None, Index))
+    return nullptr;
+  return RenamedModule;
+}
+
 //===----------------------------------------------------------------------===//
 // C API.
 //===----------------------------------------------------------------------===//