Fix caching bug in causal convolutions for cache-aware ASR models (NV…

…IDIA#7034)

nemo/collections/asr/parts/submodules/causal_convs.py

@@ -130,13 +130,16 @@ def __init__(
     def update_cache(self, x, cache=None):
         if cache is None:
             new_x = F.pad(x, pad=(self._left_padding, self._right_padding))
+            next_cache = cache
         else:
             new_x = F.pad(x, pad=(0, self._right_padding))
             new_x = torch.cat([cache, new_x], dim=-1)
             if self.cache_drop_size > 0:
-                x = x[:, :, : -self.cache_drop_size]
-            cache = torch.cat([cache[:, :, x.size(-1) :], x], dim=-1)
-        return new_x, cache
+                next_cache = new_x[:, :, : -self.cache_drop_size]
+            else:
+                next_cache = new_x
+            next_cache = next_cache[:, :, -cache.size(-1) :]
+        return new_x, next_cache
 
     def forward(self, x, cache=None):
         x, cache = self.update_cache(x, cache=cache)