[Performance] Faster clone

ghstack-source-id: 6eecbac5e946a4d93d3d6e148e8c18aaa2501b00
Pull Request resolved: #1040

tensordict/_td.py

@@ -3009,6 +3009,9 @@ def is_contiguous(self) -> bool:
         return all([value.is_contiguous() for _, value in self.items()])
 
     def _clone(self, recurse: bool = True) -> T:
+        if recurse and self.device is not None and self.device.type == "cuda":
+            return self._clone_recurse()
+
         result = TensorDict._new_unsafe(
             source={key: _clone_value(value, recurse) for key, value in self.items()},
             batch_size=self.batch_size,

tensordict/base.py

@@ -8156,6 +8156,23 @@ def cosh_(self) -> T:
         torch._foreach_cosh_(self._values_list(True, True))
         return self
 
+    def _clone_recurse(self) -> TensorDictBase:  # noqa: D417
+        keys, vals = self._items_list(True, True)
+        vals = torch._foreach_add(vals, 0)
+        items = dict(zip(keys, vals))
+        result = self._fast_apply(
+            lambda name, val: items.pop(name, None),
+            named=True,
+            nested_keys=True,
+            is_leaf=_NESTED_TENSORS_AS_LISTS,
+            propagate_lock=True,
+            filter_empty=True,
+            default=None,
+        )
+        if items:
+            result.update(items)
+        return result
+
     def add(
         self,
         other: TensorDictBase | torch.Tensor,

tensordict/nn/cudagraphs.py

@@ -302,14 +302,11 @@ def _call(*args: torch.Tensor, **kwargs: torch.Tensor):
                         torch._foreach_copy_(dests, srcs)
                     torch.cuda.synchronize()
                     self.graph.replay()
-                    if self._return_unchanged == "clone":
-                        result = self._out.clone()
-                    elif self._return_unchanged:
+                    if self._return_unchanged:
                         result = self._out
                     else:
-                        result = tree_map(
-                            lambda x: x.detach().clone() if x is not None else x,
-                            self._out,
+                        result = tree_unflatten(
+                            torch._foreach_add(self._out, 0.0), self._out_struct
                         )
                     return result
 
@@ -340,7 +337,7 @@ def _call(*args: torch.Tensor, **kwargs: torch.Tensor):
                     self.graph = torch.cuda.CUDAGraph()
                     with torch.cuda.graph(self.graph):
                         out = self.module(*self._args, **self._kwargs)
-                    self._out = out
+                    self._out, self._out_struct = tree_flatten(out)
                     self.counter += 1
                     # Check that there is not intersection between the indentity of inputs and outputs, otherwise warn
                     # user.
@@ -356,10 +353,8 @@ def _call(*args: torch.Tensor, **kwargs: torch.Tensor):
                                 f"and the identity between input and output will not match anymore. "
                                 f"Make sure you don't rely on input-output identity further in the code."
                             )
-                    if isinstance(self._out, torch.Tensor) or self._out is None:
-                        self._return_unchanged = (
-                            "clone" if self._out is not None else True
-                        )
+                    if not self._out:
+                        self._return_unchanged = True
                     else:
                         self._return_unchanged = False
                     return this_out