Refine get_cfgs method of memory optimization transpiler (#8080)

* refine get cfgs method in memory optimization transpiler

* clean code

python/paddle/v2/fluid/memory_optimization_transpiler.py

@@ -145,7 +145,6 @@ class ControlFlowGraph(object):
             if op.type() == "while" or op.type() == "while_grad":
                 continue
             block_desc = op.block()
-            self.current_block_desc = block_desc
             is_forward = i < self._forward_num
             if self.pool:
                 defs_can_optimize = filter(
@@ -208,17 +207,17 @@ def get_cfgs(input_program):
 
     while_sub_block_ids = []
     while_grad_sub_block_ids = []
-    while_op_output = set()
     while_block_id_pair = []
+    while_op_dict = {}
 
     for i in range(op_size):
         op = block_desc.op(i)
         if op.type() == "while":
             while_sub_block_ids.append(op.attr("sub_block").id)
-            while_op_output.update(op.output_arg_names())
+            while_op_dict[op.attr("sub_block").id] = op
         elif op.type() == "while_grad":
             while_grad_sub_block_ids.append(op.attr("sub_block").id)
-            while_op_output.update(op.output_arg_names())
+            while_op_dict[op.attr("sub_block").id] = op
 
     # Find while/while_grad block pair
     for grad_id in while_grad_sub_block_ids:
@@ -240,6 +239,10 @@ def get_cfgs(input_program):
         for i in range(while_grad_block_op_size):
             while_block_ops.append(while_grad_block.op(i))
 
+        while_op_output = set()
+        while_op_output.update(while_op_dict[parent_id].output_arg_names())
+        while_op_output.update(while_op_dict[grad_id].output_arg_names())
+
         ops_list.append((while_block_ops, while_block_op_size, while_op_output))
 
     # Process rest while block ops
@@ -250,9 +253,15 @@ def get_cfgs(input_program):
         for i in range(while_block_op_size):
             while_block_ops.append(while_block.op(i))
 
-        ops_list.append((while_block_ops, while_block_op_size))
+        while_op_output = set()
+        while_op_output.update(while_op_dict[parent_id].output_arg_names())
+
+        ops_list.append((while_block_ops, while_block_op_size, while_op_output))
 
-    cfgs = [ControlFlowGraph(input_program, i, j, k) for i, j, k in ops_list]
+    cfgs = [
+        ControlFlowGraph(input_program, ops, forward_num, skip_opt)
+        for ops, forward_num, skip_opt in ops_list
+    ]
     return cfgs