Fix output dtype inconsistent with input (#28649)

* fix output dtyp inconsistent with input

* refine code

python/paddle/fluid/tests/unittests/test_gather_op.py

@@ -19,6 +19,7 @@ import numpy as np
 from op_test import OpTest
 import paddle
 import paddle.fluid as fluid
+from paddle.framework import core
 
 
 def gather_numpy(x, index, axis):
@@ -298,5 +299,13 @@ class TestGathertError(unittest.TestCase):
             self.assertRaises(TypeError, test_index_type)
 
 
+class TestCheckOutType(unittest.TestCase):
+    def test_out_type(self):
+        data = paddle.static.data(shape=[16, 10], dtype='int64', name='x')
+        index = paddle.static.data(shape=[4], dtype='int64', name='index')
+        out = paddle.gather(data, index)
+        self.assertTrue(out.dtype == core.VarDesc.VarType.INT64)
+
+
 if __name__ == "__main__":
     unittest.main()

python/paddle/tensor/manipulation.py

@@ -804,7 +804,7 @@ def gather(x, index, axis=None, name=None):
         check_type(axis, 'axis', (int), 'gather')
 
     helper = LayerHelper('gather', **locals())
-    dtype = helper.input_dtype()
+    dtype = helper.input_dtype('x')
     out = helper.create_variable_for_type_inference(dtype)
     helper.append_op(
         type="gather",