!46253 Add pad operation when padding's length is equal to 0

Merge pull request !46253 from 冯一航/add_pad_null_padding_alpha

docs/api/api_python/ops/mindspore.ops.func_pad.rst

@@ -3,7 +3,7 @@ mindspore.ops.pad
 
 .. py:function:: mindspore.ops.pad(input_x, padding, mode='constant', value=None)
 
-    根据参数 `paddings` 对输入进行填充。
+    根据参数 `padding` 对输入进行填充。
 
     参数：
         - **input_x** (Tensor) - 输入Tensor，shape为 :math:`(N, *)`， :math:`*` 代表任意附加维度。

mindspore/python/mindspore/ops/function/nn_func.py

@@ -2399,7 +2399,7 @@ def _check_pad_inputs(padding):
 
 def pad(input_x, padding, mode='constant', value=None):
     r"""
-    Pads the input tensor according to the paddings.
+    Pads the input tensor according to the padding.
 
     Args:
         input_x (Tensor): Tensor of shape :math:`(N, *)`, where :math:`*` means, any number of additional dimensions.
@@ -2481,6 +2481,8 @@ def pad(input_x, padding, mode='constant', value=None):
     """
     if not isinstance(input_x, Tensor):
         raise TypeError(f"For 'pad', the type of 'input_x' must be Tensor, but got {type(input_x)}.")
+    if (isinstance(padding, (tuple, list)) and not padding) or (isinstance(padding, Tensor) and padding.shape == (0,)):
+        return input_x
     if not isinstance(padding, Tensor):
         _check_pad_inputs(padding)
         padding = Tensor(padding)