[Fix] Fix the potential NaN bug in calc_square_dist() (open-mmlab#2356)

mmcv/ops/points_sampler.py

@@ -23,16 +23,11 @@ def calc_square_dist(point_feat_a: Tensor,
         torch.Tensor: (B, N, M) Square distance between each point pair.
     """
     num_channel = point_feat_a.shape[-1]
-    # [bs, n, 1]
-    a_square = torch.sum(point_feat_a.unsqueeze(dim=2).pow(2), dim=-1)
-    # [bs, 1, m]
-    b_square = torch.sum(point_feat_b.unsqueeze(dim=1).pow(2), dim=-1)
-
-    corr_matrix = torch.matmul(point_feat_a, point_feat_b.transpose(1, 2))
-
-    dist = a_square + b_square - 2 * corr_matrix
+    dist = torch.cdist(point_feat_a, point_feat_b)
     if norm:
-        dist = torch.sqrt(dist) / num_channel
+        dist = dist / num_channel
+    else:
+        dist = torch.square(dist)
     return dist