Index: cfe/trunk/lib/Driver/ToolChains/WebAssembly.cpp
===================================================================
--- cfe/trunk/lib/Driver/ToolChains/WebAssembly.cpp
+++ cfe/trunk/lib/Driver/ToolChains/WebAssembly.cpp
@@ -62,8 +62,10 @@
     if (ToolChain.ShouldLinkCXXStdlib(Args))
       ToolChain.AddCXXStdlibLibArgs(Args, CmdArgs);
 
-    if (Args.hasArg(options::OPT_pthread))
+    if (Args.hasArg(options::OPT_pthread)) {
       CmdArgs.push_back("-lpthread");
+      CmdArgs.push_back("--shared-memory");
+    }
 
     CmdArgs.push_back("-lc");
     AddRunTimeLibs(ToolChain, ToolChain.getDriver(), CmdArgs, Args);
Index: cfe/trunk/test/Driver/wasm-toolchain.c
===================================================================
--- cfe/trunk/test/Driver/wasm-toolchain.c
+++ cfe/trunk/test/Driver/wasm-toolchain.c
@@ -41,9 +41,10 @@
 
 // Thread-related command line tests.
 
-// '-pthread' sets '-target-feature +atomics'
+// '-pthread' sets '-target-feature +atomics' and '--shared-memory'
 // RUN: %clang -### -no-canonical-prefixes -target wasm32-unknown-unknown --sysroot=/foo %s -pthread 2>&1 | FileCheck -check-prefix=PTHREAD %s
 // PTHREAD: clang{{.*}}" "-cc1" {{.*}} "-target-feature" "+atomics"
+// PTHREAD: wasm-ld{{.*}}" "-lpthread" "--shared-memory"
 
 // '-pthread' not allowed with '-mno-atomics'
 // RUN: %clang -### -no-canonical-prefixes -target wasm32-unknown-unknown --sysroot=/foo %s -pthread -mno-atomics 2>&1 | FileCheck -check-prefix=PTHREAD_NO_ATOMICS %s