[CherryPick] Cherry pick #45916 #46031 #47299 (#47610)

* [ Dy2Static ] Fix bugs when select inputs meeting different shape or undefined-var (#45916)

* fix select_input with different shape errors:
1. select_input_with_buildin_type directly return non-undefinedvar branch when meeting undefined var
2. the output shape of select_input is inferred from inputs.

* reverse the logic in select_input

* [warning] added warning message in cond block when one branch returns variable and another returns None (#46031)

* [cherry-pick] Allow manaully set py_reader name in standalone executor (#45898) (#45931)

* Allow manaully set py_reader name in standalone executor

* [BugFix] while cond receives dict as input (#47299)

* fix bugs while cond receives dict as input

* add unittest

* change flatten -> _is_sequence_except_dict

* code format
Co-authored-by: Nfeifei-111 <wuzhanfei@baidu.com>

python/paddle/fluid/tests/unittests/dygraph_to_static/test_warning.py

+#   Copyright (c) 2021 PaddlePaddle Authors. All Rights Reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import unittest
+import paddle
+import warnings
+from paddle.fluid.dygraph.dygraph_to_static.program_translator import (
+    convert_to_static,
+)
+from paddle.fluid.layers.control_flow import cond
+
+
+@paddle.jit.to_static
+def fun1():
+    a = paddle.to_tensor(1)
+    b = paddle.to_tensor(2)
+    if a > b:
+        b = paddle.to_tensor(3)
+    else:
+        b = None
+
+
+def true_fn():
+    return [paddle.to_tensor(1), [paddle.to_tensor(2), paddle.to_tensor(3)]]
+
+
+def false_fn():
+    return [paddle.to_tensor(3), [None, paddle.to_tensor(4)]]
+
+
+class TestReturnNoneInIfelse(unittest.TestCase):
+    def test_dy2static_warning(self):
+        paddle.disable_static()
+        with warnings.catch_warnings(record=True) as w:
+            warnings.simplefilter("always")
+            fun1()
+            flag = False
+            for warn in w:
+                if (
+                    issubclass(warn.category, UserWarning)
+                ) and "Set var to 'None' in ifelse block might lead to error." in str(
+                    warn.message
+                ):
+                    flag = True
+                    break
+            self.assertTrue(flag)
+
+    def test_cond_warning(self):
+        paddle.enable_static()
+        with warnings.catch_warnings(record=True) as w:
+            warnings.simplefilter("always")
+            a = paddle.to_tensor(1)
+            b = paddle.to_tensor(2)
+            cond(a < b, true_fn, false_fn, return_names=['ret1', 'ret2'])
+            flag = False
+            for warn in w:
+                if (
+                    issubclass(warn.category, UserWarning)
+                ) and "Set var to 'None' in ifelse block might lead to error." in str(
+                    warn.message
+                ):
+                    flag = True
+                    break
+            self.assertTrue(flag)
+
+
+if __name__ == '__main__':
+    unittest.main()