diff --git a/llvm/include/llvm/LTO/LTO.h b/llvm/include/llvm/LTO/LTO.h
--- a/llvm/include/llvm/LTO/LTO.h
+++ b/llvm/include/llvm/LTO/LTO.h
@@ -91,6 +91,10 @@
 Expected<std::unique_ptr<ToolOutputFile>>
 setupStatsFile(StringRef StatsFilename);
 
+/// Produce a re-ordered container for optimal multi-threaded processing.
+/// Returns indices to elements into the input array.
+std::vector<int> generateModulesOrdering(ArrayRef<BitcodeModule *> R);
+
 class LTO;
 struct SymbolResolution;
 class ThinBackendProc;
diff --git a/llvm/lib/LTO/LTO.cpp b/llvm/lib/LTO/LTO.cpp
--- a/llvm/lib/LTO/LTO.cpp
+++ b/llvm/lib/LTO/LTO.cpp
@@ -1443,10 +1443,17 @@
   auto &ModuleMap =
       ThinLTO.ModulesToCompile ? *ThinLTO.ModulesToCompile : ThinLTO.ModuleMap;
 
+  std::vector<BitcodeModule *> ModulesVec;
+  ModulesVec.reserve(ModuleMap.size());
+  for (auto &Mod : ModuleMap)
+    ModulesVec.push_back(&Mod.second);
+  std::vector<int> ModulesOrdering = generateModulesOrdering(ModulesVec);
+
   // Tasks 0 through ParallelCodeGenParallelismLevel-1 are reserved for combined
   // module and parallel code generation partitions.
   unsigned Task = RegularLTO.ParallelCodeGenParallelismLevel;
-  for (auto &Mod : ModuleMap) {
+  for (auto IndexCount : ModulesOrdering) {
+    auto &Mod = *(ModuleMap.begin() + IndexCount);
     if (Error E = BackendProc->start(Task, Mod.second, ImportLists[Mod.first],
                                      ExportLists[Mod.first],
                                      ResolvedODR[Mod.first], ThinLTO.ModuleMap))
@@ -1495,3 +1502,18 @@
   StatsFile->keep();
   return std::move(StatsFile);
 }
+
+// Compute the ordering we will process the inputs: the rough heuristic here
+// is to sort them per size so that the largest module get schedule as soon as
+// possible. This is purely a compile-time optimization.
+std::vector<int> lto::generateModulesOrdering(ArrayRef<BitcodeModule *> R) {
+  std::vector<int> ModulesOrdering;
+  ModulesOrdering.resize(R.size());
+  std::iota(ModulesOrdering.begin(), ModulesOrdering.end(), 0);
+  llvm::sort(ModulesOrdering, [&](int LeftIndex, int RightIndex) {
+    auto LSize = R[LeftIndex]->getBuffer().size();
+    auto RSize = R[RightIndex]->getBuffer().size();
+    return LSize > RSize;
+  });
+  return ModulesOrdering;
+}
diff --git a/llvm/lib/LTO/ThinLTOCodeGenerator.cpp b/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
--- a/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
+++ b/llvm/lib/LTO/ThinLTOCodeGenerator.cpp
@@ -1054,19 +1054,11 @@
     ModuleToDefinedGVSummaries[ModuleIdentifier];
   }
 
-  // Compute the ordering we will process the inputs: the rough heuristic here
-  // is to sort them per size so that the largest module get schedule as soon as
-  // possible. This is purely a compile-time optimization.
-  std::vector<int> ModulesOrdering;
-  ModulesOrdering.resize(Modules.size());
-  std::iota(ModulesOrdering.begin(), ModulesOrdering.end(), 0);
-  llvm::sort(ModulesOrdering, [&](int LeftIndex, int RightIndex) {
-    auto LSize =
-        Modules[LeftIndex]->getSingleBitcodeModule().getBuffer().size();
-    auto RSize =
-        Modules[RightIndex]->getSingleBitcodeModule().getBuffer().size();
-    return LSize > RSize;
-  });
+  std::vector<BitcodeModule *> ModulesVec;
+  ModulesVec.reserve(Modules.size());
+  for (auto &Mod : Modules)
+    ModulesVec.push_back(&Mod->getSingleBitcodeModule());
+  std::vector<int> ModulesOrdering = lto::generateModulesOrdering(ModulesVec);
 
   // Parallel optimizer + codegen
   {