shape api should not backward (#37340)

* shape api should not backward

* fix stop_gradient

* update

* update doc

python/paddle/fluid/layers/nn.py

@@ -11384,6 +11384,8 @@ def shape(input):
 
             import paddle.fluid as fluid
             import numpy as np
+            import paddle
+            paddle.enable_static()
 
             inputs = fluid.data(name="x", shape=[3, 100, 100], dtype="float32")
             output = fluid.layers.shape(inputs)
@@ -11396,6 +11398,11 @@ def shape(input):
             res = exe.run(fluid.default_main_program(), feed={'x':img}, fetch_list=[output])
             print(res) # [array([  3, 100, 100], dtype=int32)]
     """
+    if in_dygraph_mode():
+        out = _C_ops.shape(input)
+        out.stop_gradient = True
+        return out
+
     check_variable_and_dtype(input, 'input', [
         'bool', 'float16', 'float32', 'float64', 'int32', 'int64', 'complex64',
         'complex128'
@@ -11403,7 +11410,10 @@ def shape(input):
     helper = LayerHelper('shape', **locals())
     out = helper.create_variable_for_type_inference(dtype='int32')
     helper.append_op(
-        type='shape', inputs={'Input': input}, outputs={'Out': out})
+        type='shape',
+        inputs={'Input': input},
+        outputs={'Out': out},
+        stop_gradient=True)
 
     return out