message: Fix the NCHECK failure. EmitTargetElementLoop call ComputeMaxUnrollFactor when MayPreventVectorization return false. But ComputeMaxUnrollFactor call ElementsIn that works only on DenseArray. Now behave as before in that case
diff: @@ -1896,7 +1896,7 @@ bool MayPreventVectorization(const HloInstruction& hlo) {
  default:
  return false;
  }
  - } else if (hlo.opcode() == HloOpcode::kReduce) {
  + } else if (hlo.opcode() == HloOpcode::kReduce && hlo.shape().IsArray()) {
  // TODO: check if the to_apply() attribute contains instruction
  // that break LLVM vectorization.
  return false;
  