feat(imperative): enable to() to copy to device

GitOrigin-RevId: f9caf17d24fd984055b3eed48136dd429e71fb2a

imperative/python/megengine/device.py

@@ -70,7 +70,7 @@ def set_default_device(device: str = "xpux"):
         multi-threading parallelism at the operator level. For example,
         'multithread4' will compute with 4 threads. which implements
 
-        The default value is 'xpux' to specify any device available.
+        The default value is 'xpux' to specify any device available. The priority of using gpu is higher when both gpu and cpu are available.
 
         It can also be set by environmental variable `MGE_DEFAULT_DEVICE`.
     """

imperative/python/megengine/tensor.py

@@ -11,6 +11,8 @@
 import collections
 
 from .core import Tensor as _Tensor
+from .core.ops.builtin import Copy
+from .core.tensor.core import apply
 from .device import get_default_device
 
 
@@ -30,6 +32,9 @@ class Tensor(_Tensor):
     def reset_zero(self):
         self *= 0
 
+    def to(self, cn):
+        return apply(Copy(comp_node=cn), self)[0]
+
     def __getstate__(self):
         r""" __getstate__ will be called for pickle serialization or deep copy
         """

imperative/python/test/unit/functional/test_tensor.py

@@ -322,6 +322,8 @@ def copy_test(dst, src):
     x = tensor(data, device=src)
     y = F.copy(x, dst)
     assert np.allclose(data, y.numpy())
+    z = x.to(dst)
+    assert np.allclose(data, z.numpy())
 
 
 @pytest.mark.skipif(