only import 'alt_cuda_corr' when 'AlternateCorrBlock' is used

Author: christian-rauch

core/corr.py

@@ -2,12 +2,6 @@
 import torch.nn.functional as F
 from utils.utils import bilinear_sampler, coords_grid
 
-try:
-    import alt_cuda_corr
-except:
-    # alt_cuda_corr is not compiled
-    pass
-
 
 class CorrBlock:
     def __init__(self, fmap1, fmap2, num_levels=4, radius=4):
@@ -62,6 +56,9 @@ def corr(fmap1, fmap2):
 
 class AlternateCorrBlock:
     def __init__(self, fmap1, fmap2, num_levels=4, radius=4):
+        import alt_cuda_corr
+        self.alt_corr_fwd = alt_cuda_corr.forward
+
         self.num_levels = num_levels
         self.radius = radius