Index: llvm/lib/Target/X86/X86ISelLowering.cpp
===================================================================
--- llvm/lib/Target/X86/X86ISelLowering.cpp
+++ llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -364,8 +364,13 @@
   // encoding.
   setOperationPromotedToType(ISD::CTTZ           , MVT::i8   , MVT::i32);
   setOperationPromotedToType(ISD::CTTZ_ZERO_UNDEF, MVT::i8   , MVT::i32);
-  if (!Subtarget.hasBMI()) {
-    setOperationAction(ISD::CTTZ           , MVT::i16  , Custom);
+
+  if (Subtarget.hasBMI()) {
+    // Promote the i16 zero undef variant and force it on up to i32 when tzcnt
+    // is enabled.
+    setOperationPromotedToType(ISD::CTTZ_ZERO_UNDEF, MVT::i16, MVT::i32);
+  } else {
+    setOperationAction(ISD::CTTZ, MVT::i16, Custom);
     setOperationAction(ISD::CTTZ           , MVT::i32  , Custom);
     setOperationAction(ISD::CTTZ_ZERO_UNDEF, MVT::i16  , Legal);
     setOperationAction(ISD::CTTZ_ZERO_UNDEF, MVT::i32  , Legal);
Index: llvm/test/CodeGen/X86/clz.ll
===================================================================
--- llvm/test/CodeGen/X86/clz.ll
+++ llvm/test/CodeGen/X86/clz.ll
@@ -56,12 +56,14 @@
 ;
 ; X86-CLZ-LABEL: cttz_i16:
 ; X86-CLZ:       # %bb.0:
-; X86-CLZ-NEXT:    tzcntw {{[0-9]+}}(%esp), %ax
+; X86-CLZ-NEXT:    tzcntl {{[0-9]+}}(%esp), %eax
+; X86-CLZ-NEXT:    # kill: def $ax killed $ax killed $eax
 ; X86-CLZ-NEXT:    retl
 ;
 ; X64-CLZ-LABEL: cttz_i16:
 ; X64-CLZ:       # %bb.0:
-; X64-CLZ-NEXT:    tzcntw %di, %ax
+; X64-CLZ-NEXT:    tzcntl %edi, %eax
+; X64-CLZ-NEXT:    # kill: def $ax killed $ax killed $eax
 ; X64-CLZ-NEXT:    retq
   %tmp = call i16 @llvm.cttz.i16( i16 %x, i1 true )
   ret i16 %tmp