Tracer does not hold op any more

test=develop

python/paddle/fluid/dygraph/tracer.py

@@ -24,7 +24,7 @@ __all__ = ['Tracer']
 
 
 def release_op(op):
-    del framework._dygraph_tracer()._ops[op._trace_id]
+    del framework._dygraph_tracer()._ops[op._trace_id].inputs
 
 
 class Tracer(core.Tracer):
@@ -46,11 +46,34 @@ class Tracer(core.Tracer):
         return list((item for name, item in six.iteritems(self._vars)
                      if isinstance(item, framework.Parameter)))
 
-    def trace_op(self, op, stop_gradient=False):
+    def trace_op(self, op, inputs, outputs, stop_gradient=False):
+        # TODO(minqiyang): remove this line after we take apart all
+        # backward grads and forward variables
+        op.inputs = inputs
+        inps = defaultdict(list)
+        for k, vars in six.iteritems(inputs):
+            if isinstance(vars, framework.Variable):
+                op.previous_ops.append(vars.op)
+                inps[k].append(vars._ivar)
+            elif isinstance(vars, list) or isinstance(vars, tuple):
+                for var in vars:
+                    op.previous_ops.append(var.op)
+                    inps[k].append(var._ivar)
+
+        outs = defaultdict(list)
+        for k, vars in six.iteritems(outputs):
+            if isinstance(vars, framework.Variable):
+                vars.op = op
+                outs[k].append(vars._ivar)
+            elif isinstance(vars, list) or isinstance(vars, tuple):
+                for var in vars:
+                    var.op = op
+                    outs[k].append(var._ivar)
+
         # record op's trace id
         op.iop._trace_id = self._trace_id
 
-        backward_refs = self.trace(op.iop, op.inputs, op.outputs, op.attrs,
+        backward_refs = self.trace(op.iop, inps, outs, op.attrs,
                                    framework._current_expected_place(),
                                    stop_gradient)
 
@@ -65,10 +88,10 @@ class Tracer(core.Tracer):
                 # TODO(minqiyang): remove all inputs and outputs after separate
                 # var and grad
                 op.backward_refs = defaultdict(list)
-                for k, v in six.iteritems(op.inputs):
+                for k, v in six.iteritems(inputs):
                     if k in backward_refs:
-                        op.backward_refs[k] = op.inputs[k]
+                        op.backward_refs[k] = inputs[k]
 
-                for k, v in six.iteritems(op.outputs):
+                for k, v in six.iteritems(outputs):
                     if k in backward_refs:
-                        op.backward_refs[k] = op.outputs[k]
+                        op.backward_refs[k] = outputs[k]

python/paddle/fluid/framework.py

@@ -411,6 +411,7 @@ class Variable(object):
                     if persistable else False)
             if persistable:
                 _dygraph_tracer().trace_var(name, self)
+            self.op = None
         else:
             self.error_clip = error_clip
 
@@ -939,26 +940,9 @@ class Operator(object):
                 raise ValueError(
                     "`type` to initialized an Operator can not be None.")
             self.iop = core.OpBase(type)
+            self.previous_ops = []
 
-            # TODO(minqiyang): remove these lines after we take apart all
-            # backward grads and forward variables
-            self.inputs = defaultdict(list)
-            if inputs is not None:
-                for k, v in six.iteritems(inputs):
-                    if isinstance(v, Variable):
-                        self.inputs[k].append(v._ivar)
-                    elif isinstance(v, list) or isinstance(v, tuple):
-                        self.inputs[k].extend([var._ivar for var in v])
-
-            self.outputs = defaultdict(list)
-            if outputs is not None:
-                for k, v in six.iteritems(outputs):
-                    if isinstance(v, Variable):
-                        self.outputs[k].append(v._ivar)
-                    elif isinstance(v, list) or isinstance(v, tuple):
-                        self.outputs[k].extend([var._ivar for var in v])
-
-            self.attrs = attrs if attrs else {}
+            self.attrs = attrs
         else:
             self.block = block
             self.desc = desc
@@ -1647,15 +1631,18 @@ class Block(object):
                 block=self,
                 desc=None,
                 type=kwargs.get("type", None),
-                inputs=kwargs.get("inputs", None),
-                outputs=kwargs.get("outputs", None),
-                attrs=kwargs.get("attrs", None))
+                inputs=None,
+                outputs=None,
+                attrs=kwargs.get("attrs", {}))
 
             # record ops in tracer rather than blocks
             #
             # TODO(minqiyang): add op stop_gradient support in static mode too.
             # currently, we only support stop_gradient in dygraph mode.
-            _dygraph_tracer().trace_op(op, kwargs.get("stop_gradient", False))
+            _dygraph_tracer().trace_op(op,
+                                       kwargs.get("inputs", {}),
+                                       kwargs.get("outputs", {}),
+                                       kwargs.get("stop_gradient", False))
         else:
             op_desc = self.desc.append_op()
             op = Operator(
@@ -1719,10 +1706,14 @@ class Block(object):
                 self,
                 None,
                 type=kwargs.get("type", None),
-                inputs=kwargs.get("inputs", None),
-                outputs=kwargs.get("outputs", None),
-                attrs=kwargs.get("attrs", None))
-            _dygraph_tracer().trace_op(op, kwargs.get("stop_gradient", False))
+                inputs=None,
+                outputs=None,
+                attrs=kwargs.get("attrs", {}))
+
+            _dygraph_tracer().trace_op(op,
+                                       kwargs.get("inputs", {}),
+                                       kwargs.get("outputs", {}),
+                                       kwargs.get("stop_gradient", False))
         else:
             op_desc = self.desc._prepend_op()
             op = Operator(