[Enhancement] Refine the implementation of NMS op in Ascend device (#2658)

mmcv/ops/csrc/pytorch/npu/nms_npu.cpp

@@ -4,10 +4,7 @@ using namespace NPU_NAME_SPACE;
 using namespace std;
 
 Tensor nms_npu(Tensor boxes, Tensor scores, float iou_threshold, int offset) {
-  at::Tensor boxed_offest = at_npu::native::OpPreparation::ApplyTensor(boxes);
-  at::Tensor ones_tensor =
-      at_npu::native::OpPreparation::ApplyTensor(boxes).fill_(1);
-  at::add_out(boxed_offest, boxes, ones_tensor, offset);
+  int64_t offset_64 = offset;
   at::Tensor iou_threshold_y = at_npu::native::OpPreparation::ApplyTensor(
                                    {}, boxes.options().dtype(at::kFloat), boxes)
                                    .fill_(iou_threshold);
@@ -29,6 +26,7 @@ Tensor nms_npu(Tensor boxes, Tensor scores, float iou_threshold, int offset) {
       .Input(max_outputsize_y)
       .Input(iou_threshold_y)
       .Input(scores_threshold_y)
+      .Attr("offset", offset_64)
       .Output(output)
       .Run();
   auto outputsizeBool = at::gt(output, -1);