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/clang-translation.c
===================================================================
--- test/Driver/clang-translation.c
+++ test/Driver/clang-translation.c
@@ -318,28 +318,29 @@
 // ANDROID-X86_64: "-target-cpu" "x86-64"
 // ANDROID-X86_64: "-target-feature" "+sse4.2"
 // ANDROID-X86_64: "-target-feature" "+popcnt"
+// ANDROID-X86_64: "-target-feature" "+mcx16"

 // RUN: %clang -target mips-linux-gnu -### -S %s 2>&1 | \
 // RUN: FileCheck -check-prefix=MIPS %s
 // MIPS: clang
 // MIPS: "-cc1"
 // MIPS: "-target-cpu" "mips32r2"
 // MIPS: "-mfloat-abi" "hard"

 // RUN: %clang -target mipsisa32r6-linux-gnu -### -S %s 2>&1 | \
 // RUN: FileCheck -check-prefix=MIPSR6 %s
 // MIPSR6: clang
 // MIPSR6: "-cc1"
 // MIPSR6: "-target-cpu" "mips32r6"
 // MIPSR6: "-mfloat-abi" "hard"

 // RUN: %clang -target mipsel-linux-gnu -### -S %s 2>&1 | \
 // RUN: FileCheck -check-prefix=MIPSEL %s
 // MIPSEL: clang
 // MIPSEL: "-cc1"
 // MIPSEL: "-target-cpu" "mips32r2"
 // MIPSEL: "-mfloat-abi" "hard"

 // RUN: %clang -target mipsisa32r6el-linux-gnu -### -S %s 2>&1 | \
 // RUN: FileCheck -check-prefix=MIPSR6EL %s
 // MIPSR6EL: clang