Modify tmp var name prefix in dygraph (#25280)

* Modify tmp var name prefix in dygraph test=develop

* refine comment test=develop

paddle/fluid/imperative/tests/test_tracer.cc

@@ -285,6 +285,11 @@ TEST(test_tracer, test_unique_name_generator) {
   auto fc_2 = tracer.GenerateUniqueName("fc");
   ASSERT_STREQ("fc_0", fc_1.c_str());
   ASSERT_STREQ("fc_1", fc_2.c_str());
+  // use `eager_tmp` as key if not specify it.
+  auto tmp_var_2 = tracer.GenerateUniqueName();
+  ASSERT_STREQ("eager_tmp_2", tmp_var_2.c_str());
+  auto tmp_var_3 = tracer.GenerateUniqueName("eager_tmp");
+  ASSERT_STREQ("eager_tmp_3", tmp_var_3.c_str());
 }
 
 TEST(test_tracer, test_current_tracer) {

paddle/fluid/imperative/tracer.h

@@ -76,7 +76,14 @@ class Tracer {
     return program_desc_tracer_.get();
   }
 
-  std::string GenerateUniqueName(std::string key = "tmp") {
+  // Note(Aurelius84): The `tmp` is used as prefix key while naming a temporary
+  // intermediate var both in imperative and static mode. But the
+  // `UniqueNameGenerator` in C++ and `unique_name.py` in Python doesn't share
+  // the same auto-increment id. It will create a variable repeatedly with same
+  // name like `tmp_0` in some cases when transform dygraph into static layers.
+  // So we modify the default prefix key into `eager_tmp` to distinguish with
+  // static graph.
+  std::string GenerateUniqueName(std::string key = "eager_tmp") {
     return generator_->Generate(key);
   }
 

paddle/fluid/pybind/imperative.cc

@@ -873,7 +873,7 @@ void BindImperative(py::module *m_ptr) {
            &imperative::Tracer::GetProgramDescTracer,
            py::return_value_policy::reference)
       .def("_generate_unique_name", &imperative::Tracer::GenerateUniqueName,
-           py::arg("key") = "tmp")
+           py::arg("key") = "eager_tmp")
       .def("trace",
            [](imperative::Tracer &self, const std::string &type,
               const PyNameVarBaseMap &ins, const PyNameVarBaseMap &outs,

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

@@ -43,3 +43,18 @@ class TestUniqueName(unittest.TestCase):
             name3 = fluid.unique_name.generate('tmp')
             self.assertNotEqual(name1, name2)
             self.assertEqual(name1[-2:], name3[-2:])
+
+
+class TestImperativeUniqueName(unittest.TestCase):
+    def test_name_generator(self):
+        with fluid.dygraph.guard():
+            tracer = fluid.framework._dygraph_tracer()
+            tmp_var_0 = tracer._generate_unique_name()
+            self.assertEqual(tmp_var_0, "eager_tmp_0")
+
+            tmp_var_1 = tracer._generate_unique_name("eager_tmp")
+            self.assertEqual(tmp_var_1, "eager_tmp_1")
+
+
+if __name__ == '__main__':
+    unittest.main()