Index: lib/Driver/ToolChains/Arch/X86.cpp
===================================================================
--- lib/Driver/ToolChains/Arch/X86.cpp
+++ lib/Driver/ToolChains/Arch/X86.cpp
@@ -135,10 +135,11 @@
     if (ArchType == llvm::Triple::x86_64) {
       Features.push_back("+sse4.2");
       Features.push_back("+popcnt");
+      Features.push_back("+mcx16");
     } else
       Features.push_back("+ssse3");
   }

   // Translate the high level `-mretpoline` flag to the specific target feature
   // flags. We also detect if the user asked for retpoline external thunks but
   // failed to ask for retpolines themselves (through any of the different
Index: test/Driver/android-default-x86_64.c
===================================================================
--- /dev/null
+++ test/Driver/android-default-x86_64.c
@@ -0,0 +1,2 @@
+// RUN: %clang -### -target x86_64-unknown-linux-android -c %s 2>&1 | FileCheck %s
+// CHECK: "-mcx16"