[X86] LowerShift - use DAG::getNegative() helper. NFC.

Author: RKSimon

llvm/lib/Target/X86/X86ISelLowering.cpp

@@ -29374,10 +29374,8 @@ static SDValue LowerShift(SDValue Op, const X86Subtarget &Subtarget,
   // +ve/-ve Amt = shift left/right.
   if (Subtarget.hasXOP() && (VT == MVT::v2i64 || VT == MVT::v4i32 ||
                              VT == MVT::v8i16 || VT == MVT::v16i8)) {
-    if (Opc == ISD::SRL || Opc == ISD::SRA) {
-      SDValue Zero = DAG.getConstant(0, dl, VT);
-      Amt = DAG.getNode(ISD::SUB, dl, VT, Zero, Amt);
-    }
+    if (Opc == ISD::SRL || Opc == ISD::SRA)
+      Amt = DAG.getNegative(Amt, dl, VT);
     if (Opc == ISD::SHL || Opc == ISD::SRL)
       return DAG.getNode(X86ISD::VPSHL, dl, VT, R, Amt);
     if (Opc == ISD::SRA)