Index: wasm/LTO.cpp
===================================================================
--- wasm/LTO.cpp
+++ wasm/LTO.cpp
@@ -47,8 +47,12 @@
   C.Options.FunctionSections = true;
   C.Options.DataSections = true;
 
-  // Wasm currently only supports ThreadModel::Single
-  C.Options.ThreadModel = ThreadModel::Single;
+  // When shared memory is disabled wasm doesn't support atomics operations.
+  // Setting the thead model based on the SharedMemory option seems like
+  // reasonable default.  Idealy the bitcode metadata would set this on
+  // a per function basis instead.
+  C.Options.ThreadModel =
+      Config->SharedMemory ? ThreadModel::POSIX : ThreadModel::Single;
 
   C.DisableVerify = Config->DisableVerify;
   C.DiagHandler = diagnosticHandler;