fix gc bug in conditional block (#16673)

test=develop

paddle/fluid/operators/controlflow/conditional_block_op.cc

@@ -12,6 +12,9 @@ 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. */
 #include <algorithm>
+#include <memory>
+#include <string>
+#include <vector>
 #include "paddle/fluid/framework/executor.h"
 #include "paddle/fluid/framework/op_registry.h"
 #include "paddle/fluid/framework/var_type.h"
@@ -174,24 +177,41 @@ class ConditionalBlockGradOp : public ConditionalOp {
 
       framework::Executor exec(dev_place);
       auto *block = Attr<framework::BlockDesc *>("sub_block");
-      exec.Run(*block->Program(), &cur_scope, block->ID(), false);
 
-      AssignLocalGradientToGlobal(dev_place, cur_scope, Inputs("Input"),
-                                  Outputs(framework::GradVarName("Input")));
+      const auto &ins = Inputs("Input");
+      const auto &d_ins = Outputs(framework::GradVarName("Input"));
+      const auto &conds = Inputs("Cond");
+      const auto &d_conds = Outputs(framework::GradVarName("Cond"));
+
+      std::vector<std::string> ins_conds_grads;
+      ins_conds_grads.reserve(ins.size() + conds.size());
+      for (auto &in : ins) {
+        ins_conds_grads.emplace_back(framework::GradVarName(in));
+      }
+      for (auto &cond : conds) {
+        ins_conds_grads.emplace_back(framework::GradVarName(cond));
+      }
+
+      exec.Run(*block->Program(), &cur_scope, block->ID(), false, true,
+               ins_conds_grads);
+
+      AssignLocalGradientToGlobal(dev_place, cur_scope, ins_conds_grads.data(),
+                                  ins.size(), d_ins);
 
-      AssignLocalGradientToGlobal(dev_place, cur_scope, Inputs("Cond"),
-                                  Outputs(framework::GradVarName("Cond")));
+      AssignLocalGradientToGlobal(dev_place, cur_scope,
+                                  ins_conds_grads.data() + ins.size(),
+                                  conds.size(), d_conds);
     }
   }
 
  private:
   void AssignLocalGradientToGlobal(
       const platform::Place &place, const framework::Scope &cur_scope,
-      const std::vector<std::string> &p_names,
+      const std::string *p_grad_names, size_t p_grad_names_num,
       const std::vector<std::string> &pg_names) const {
-    for (size_t i = 0; i < p_names.size(); ++i) {
+    for (size_t i = 0; i < p_grad_names_num; ++i) {
       auto out_grad_name = pg_names[i];
-      auto in_grad_name = framework::GradVarName(p_names[i]);
+      const auto &in_grad_name = p_grad_names[i];
       auto *in_var = cur_scope.FindVar(in_grad_name);
       if (in_var == nullptr) {
         continue;

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

+# Copyright (c) 2019 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 paddle.fluid as fluid
+import unittest
+
+fluid.core._set_eager_deletion_mode(0.0, 1.0, True)
+
+from test_conditional_block import *
+
+if __name__ == '__main__':
+    unittest.main()