Index: llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
===================================================================
--- llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
+++ llvm/trunk/lib/Target/X86/X86ISelLowering.cpp
@@ -43890,6 +43890,18 @@
          RC.hasSuperClassEq(&X86::VR512RegClass);
 }
 
+/// Check if \p RC is a mask register class.
+/// I.e., VK* or one of their variant.
+static bool isVKClass(const TargetRegisterClass &RC) {
+  return RC.hasSuperClassEq(&X86::VK1RegClass) ||
+         RC.hasSuperClassEq(&X86::VK2RegClass) ||
+         RC.hasSuperClassEq(&X86::VK4RegClass) ||
+         RC.hasSuperClassEq(&X86::VK8RegClass) ||
+         RC.hasSuperClassEq(&X86::VK16RegClass) ||
+         RC.hasSuperClassEq(&X86::VK32RegClass) ||
+         RC.hasSuperClassEq(&X86::VK64RegClass);
+}
+
 std::pair<unsigned, const TargetRegisterClass *>
 X86TargetLowering::getRegForInlineAsmConstraint(const TargetRegisterInfo *TRI,
                                                 StringRef Constraint,
@@ -44204,6 +44216,22 @@
       Res.first = 0;
       Res.second = nullptr;
     }
+  } else if (isVKClass(*Class)) {
+    if (VT == MVT::i1)
+      Res.second = &X86::VK1RegClass;
+    else if (VT == MVT::i8)
+      Res.second = &X86::VK8RegClass;
+    else if (VT == MVT::i16)
+      Res.second = &X86::VK16RegClass;
+    else if (VT == MVT::i32)
+      Res.second = &X86::VK32RegClass;
+    else if (VT == MVT::i64)
+      Res.second = &X86::VK64RegClass;
+    else {
+      // Type mismatch and not a clobber: Return an error;
+      Res.first = 0;
+      Res.second = nullptr;
+    }
   }
 
   return Res;
Index: llvm/trunk/test/CodeGen/X86/pr41678.ll
===================================================================
--- llvm/trunk/test/CodeGen/X86/pr41678.ll
+++ llvm/trunk/test/CodeGen/X86/pr41678.ll
@@ -0,0 +1,22 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc < %s -O0 -mtriple=i386-pc-linux-gnu -mattr=avx512f | FileCheck %s
+
+define void @a() {
+; CHECK-LABEL: a:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    subl $2, %esp
+; CHECK-NEXT:    .cfi_def_cfa_offset 6
+; CHECK-NEXT:    #APP
+; CHECK-NEXT:    #NO_APP
+; CHECK-NEXT:    kmovw %k6, %eax
+; CHECK-NEXT:    movw %ax, %cx
+; CHECK-NEXT:    movw %cx, (%esp)
+; CHECK-NEXT:    addl $2, %esp
+; CHECK-NEXT:    .cfi_def_cfa_offset 4
+; CHECK-NEXT:    retl
+entry:
+  %b = alloca i16, align 2
+  %0 = call i16 asm "", "={k6},~{dirflag},~{fpsr},~{flags}"() #1
+  store i16 %0, i16* %b, align 2
+  ret void
+}