Index: lib/LTO/ThinLTOCodeGenerator.cpp
===================================================================
--- lib/LTO/ThinLTOCodeGenerator.cpp
+++ lib/LTO/ThinLTOCodeGenerator.cpp
@@ -822,8 +822,12 @@
  * Perform ThinLTO CodeGen.
  */
 std::unique_ptr<MemoryBuffer> ThinLTOCodeGenerator::codegen(Module &TheModule) {
-  initTMBuilder(TMBuilder, Triple(TheModule.getTargetTriple()));
-  return codegenModule(TheModule, *TMBuilder.create());
+  // Create local copy of TMBuilder as ThinLTOCodeGenerator::codegen needs to
+  // be thread safe and initTMBuilder below is not thread safe on same object
+  TargetMachineBuilder moduleTMBuilder(TMBuilder);
+
+  initTMBuilder(moduleTMBuilder, Triple(TheModule.getTargetTriple()));
+  return codegenModule(TheModule, *moduleTMBuilder.create());
 }
 
 /// Write out the generated object file, either from CacheEntryPath or from