Prefer NUW flags as per https://alive2.llvm.org/ce/z/_V5s8p

Author: paulwalker-arm

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -10620,8 +10620,12 @@ SDValue DAGCombiner::visitSHL(SDNode *N) {
 
   // fold (shl (X * vscale(VS0)), C1) -> (X * vscale(VS0 << C1))
   if (N1C && sd_match(N0, m_Mul(m_Value(X), m_VScale(m_ConstInt(VS0))))) {
+    SDNodeFlags Flags;
+    Flags.setNoUnsignedWrap(N->getFlags().hasNoUnsignedWrap() &&
+                            N0->getFlags().hasNoUnsignedWrap());
+
     SDValue VScale = DAG.getVScale(DL, VT, VS0 << N1C->getAPIntValue());
-    return DAG.getNode(ISD::MUL, DL, VT, X, VScale);
+    return DAG.getNode(ISD::MUL, DL, VT, X, VScale, Flags);
   }
 
   // Fold (shl step_vector(C0), C1) to (step_vector(C0 << C1)).