diff -ru llvm-8.0.0.src.orig/lib/LTO/LTO.cpp llvm-8.0.0.src/lib/LTO/LTO.cpp
--- llvm-8.0.0.src.orig/lib/LTO/LTO.cpp	2019-04-12 09:08:36.531911405 +0000
+++ llvm-8.0.0.src/lib/LTO/LTO.cpp	2019-04-12 09:11:23.783949538 +0000
@@ -953,7 +953,6 @@
 
 namespace {
 class InProcessThinBackend : public ThinBackendProc {
-  ThreadPool BackendThreadPool;
   AddStreamFn AddStream;
   NativeObjectCache Cache;
   std::set<GlobalValue::GUID> CfiFunctionDefs;
@@ -969,7 +968,6 @@
       const StringMap<GVSummaryMapTy> &ModuleToDefinedGVSummaries,
       AddStreamFn AddStream, NativeObjectCache Cache)
       : ThinBackendProc(Conf, CombinedIndex, ModuleToDefinedGVSummaries),
-        BackendThreadPool(ThinLTOParallelismLevel),
         AddStream(std::move(AddStream)), Cache(std::move(Cache)) {
     for (auto &Name : CombinedIndex.cfiFunctionDefs())
       CfiFunctionDefs.insert(
@@ -1027,32 +1025,12 @@
     assert(ModuleToDefinedGVSummaries.count(ModulePath));
     const GVSummaryMapTy &DefinedGlobals =
         ModuleToDefinedGVSummaries.find(ModulePath)->second;
-    BackendThreadPool.async(
-        [=](BitcodeModule BM, ModuleSummaryIndex &CombinedIndex,
-            const FunctionImporter::ImportMapTy &ImportList,
-            const FunctionImporter::ExportSetTy &ExportList,
-            const std::map<GlobalValue::GUID, GlobalValue::LinkageTypes>
-                &ResolvedODR,
-            const GVSummaryMapTy &DefinedGlobals,
-            MapVector<StringRef, BitcodeModule> &ModuleMap) {
-          Error E = runThinLTOBackendThread(
+    return runThinLTOBackendThread(
               AddStream, Cache, Task, BM, CombinedIndex, ImportList, ExportList,
               ResolvedODR, DefinedGlobals, ModuleMap);
-          if (E) {
-            std::unique_lock<std::mutex> L(ErrMu);
-            if (Err)
-              Err = joinErrors(std::move(*Err), std::move(E));
-            else
-              Err = std::move(E);
-          }
-        },
-        BM, std::ref(CombinedIndex), std::ref(ImportList), std::ref(ExportList),
-        std::ref(ResolvedODR), std::ref(DefinedGlobals), std::ref(ModuleMap));
-    return Error::success();
   }
 
   Error wait() override {
-    BackendThreadPool.wait();
     if (Err)
       return std::move(*Err);
     else