update

paddle/pybind/protobuf.cc

@@ -236,15 +236,25 @@ void BindOpDesc(py::module &m) {
       .value("BLOCK", AttrType::BLOCK);
 
   py::class_<OpDescBind> op_desc(m, "OpDesc", "");
-  op_desc.def("type", &OpDescBind::Type)
+  op_desc
+      .def("__init__",
+           [](OpDescBind &self, const std::string &type,
+              const VariableNameMap &inputs, const VariableNameMap &outputs,
+              const AttributeMap &attrs) {
+             new (&self) OpDescBind(type, inputs, outputs, attrs);
+           })
+      .def("type", &OpDescBind::Type)
       .def("set_type", &OpDescBind::SetType)
       .def("input", &OpDescBind::Input)
       .def("input_names", &OpDescBind::InputNames)
-      .def("set_input", &OpDescBind::SetInput)
       .def("output", &OpDescBind::Output)
       .def("output_names", &OpDescBind::OutputNames)
-      .def("output_arg_names", &OpDescBind::OutputArgumentNames)
+      .def("set_input", &OpDescBind::SetInput)
       .def("set_output", &OpDescBind::SetOutput)
+      .def("input_arg_names", &OpDescBind::InputArgumentNames)
+      .def("output_arg_names", &OpDescBind::OutputArgumentNames)
+      .def("rename_input", &OpDescBind::RenameInput)
+      .def("rename_output", &OpDescBind::RenameOutput)
       .def("has_attr", &OpDescBind::HasAttr)
       .def("attr_type", &OpDescBind::GetAttrType)
       .def("attr_names", &OpDescBind::AttrNames)

paddle/pybind/pybind.cc

@@ -314,6 +314,7 @@ All parameter, weight, gradient are variables in Paddle.
     InferenceOptimize(*(origin.Proto()), &pruned_desc);
     return new ProgramDescBind(pruned_desc);
   });
+  m.def("get_empty_var_name", []() { return framework::kEmptyVarName; });
   m.def_submodule(
        "var_names",
        "The module will return special predefined variable name in Paddle")

python/paddle/v2/fluid/backward.py

@@ -5,8 +5,19 @@ import collections
 __all__ = ['append_backward_ops']
 
 
-def backward_impl(block, target_block, no_grad_set, grad_to_var, callback):
+def rename_arg(op_desc_list, old_name, new_name, begin_idx=None, end_idx=None):
+    if begin_idx is None:
+        begin_idx = 0
+    if end_idx is None:
+        end_idx = len(op_desc_list)
+    for i in range(begin_idx, end_idx):
+        op_desc_list[i].rename_input(old_name, new_name)
+        op_desc_list[i].rename_output(old_name, new_name)
+
+
+def backward_impl(block, target_block, no_grad_set, callback=None):
     grad_op_descs = []
+    grad_to_var = {}
     program = block.program
     for each_op in block.ops:
         grad_sub_block_list = []
@@ -14,8 +25,7 @@ def backward_impl(block, target_block, no_grad_set, grad_to_var, callback):
             sub_block_idx = each_op.block_attr("sub_block")
             sub_block = program.block(sub_block_idx)
             grad_sub_block = program.create_block(parent_idx=sub_block_idx)
-            backward_impl(sub_block, grad_sub_block, no_grad_set, grad_to_var,
-                          callback)
+            backward_impl(sub_block, grad_sub_block, no_grad_set, callback)
             grad_sub_block_list.append(grad_sub_block)
         grad_op_desc = core.get_grad_op_desc(each_op.desc,
                                              no_grad_set[block.idx],
@@ -25,16 +35,53 @@ def backward_impl(block, target_block, no_grad_set, grad_to_var, callback):
     # flatten grad_op_descs
     grad_op_descs = [op for sublist in grad_op_descs for op in sublist]  # ?????
 
-    output_vars = collections.defaultdict(list)
+    pending_sum_ops = []
+    var_rename_count = collections.defaultdict(int)
+    var_inputs = collections.defaultdict(list)
     for pos, op_desc in enumerate(grad_op_descs):
+        for var_name in op_desc.input_arg_names():
+            if len(var_inputs[var_name]) > 1:
+                pending_sum_ops.append((core.OpDesc(
+                    type="sum_op",
+                    inputs=var_inputs[var_name],
+                    output=[var_name],
+                    attrs={}), pos))
+                var_inputs[var_name] = [var_name]
         for var_name in op_desc.output_arg_names():
-            output_vars[var_name].append(pos)
-    for var_name, poses in output_vars.iteritems():
-        if len(poses) == 1:
+            if len(var_inputs[var_name]) == 0:
+                # it's the first time we get the variable
+                var_inputs[var_name] = var_name
+            else:
+                if len(var_inputs[var_name] == 1):
+                    new_name = var_name + "@RENAME@" + \
+                        str(var_rename_count[var_name])
+                    var_rename_count[var_name] = var_rename_count[var_name] + 1
+                    # rename original var_name
+                    var_inputs[var_name][0] = new_name
+                    rename_arg(grad_op_descs, var_name, new_name, 0, pos)
+                    rename_arg(pending_sum_ops, var_name, new_name)
+
+                new_name = var_name + "@RENAME@" + \
+                    str(var_rename_count[var_name])
+                var_rename_count[var_name] = var_rename_count[var_name] + 1
+                op_desc.rename_output(var_name, new_name)
+                var_inputs[var_name].append(new_name)
+    for var_name, inputs in var_inputs.iteritems():
+        if len(inputs) > 1:
+            pending_sum_ops.append((core.OpDesc(
+                type="sum_op", inputs=inputs, outputs=var_name, attrs={}),
+                                    len(grad_op_descs)))
+    # 根据append的顺序可以看出pending_sum_ops一定是根据sum_op的插入位置排序的
+    for p in reversed(pending_sum_ops):
+        grad_op_descs.insert(p[1], p[0])
+    # create new gradient variables in the target block
+    for op_desc in grad_op_descs:
+        for grad_var_name in op_desc.output_arg_names():
+            if target_block.has_var(
+                    grad_var_name) or grad_var_name == core.get_empty_var_name(
+                    ):
                 continue
-        renamed_list = []
-        for pos in reversed(sorted(poses)):
-            new_name = var_name + "@RENAMED@" + len(renamed_list)
+            target_block.var(grad_var_name)
 
 
 def append_backward_ops(loss, parameter_list=None, no_grad_set=None):