[SelectionDAG] Update canCreateUndefOrPoison to handle VECTOR_COMPRESS case

Author: Michael-Chen-NJU

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

@@ -5702,6 +5702,11 @@ bool SelectionDAG::canCreateUndefOrPoison(SDValue Op, const APInt &DemandedElts,
     return false;
   }
 
+  case ISD::VECTOR_COMPRESS:
+    // Return true only if undef is checked and at least one element is
+    // demanded.
+    return !PoisonOnly && !DemandedElts.isZero();
+
   default:
     // Allow the target to implement this method for its nodes.
     if (Opcode >= ISD::BUILTIN_OP_END || Opcode == ISD::INTRINSIC_WO_CHAIN ||