polish more

test=develop

paddle/fluid/imperative/tracer.cc

@@ -164,28 +164,30 @@ std::vector<VarBase*> Tracer::PyTrace(OpBase* op,
                                       const std::vector<VarBase*>& inputs,
                                       bool stop_gradient) {
   VLOG(3) << "py_trace";
-  op->input_vars_["X"] = inputs;
-  op->output_vars_["Out"] = PyLayer::Apply(op->forward_id_, inputs);
+  op->input_vars_[PyLayer::kFwdInp] = inputs;
+  op->output_vars_[PyLayer::kFwdOut] = PyLayer::Apply(op->forward_id_, inputs);
   for (VarBase* inp : inputs) {
     if (inp->pre_op_) {
-      op->pre_ops_["X"].push_back(inp->pre_op_);
-      op->pre_ops_out_idx_["X"].push_back(inp->pre_op_out_idx_);
+      op->pre_ops_[PyLayer::kFwdInp].push_back(inp->pre_op_);
+      op->pre_ops_out_idx_[PyLayer::kFwdInp].push_back(inp->pre_op_out_idx_);
     } else {
-      op->pre_ops_["X"].push_back(nullptr);
+      op->pre_ops_[PyLayer::kFwdInp].push_back(nullptr);
     }
   }
 
-  auto& outputs = op->output_vars_["Out"];
+  auto& outputs = op->output_vars_[PyLayer::kFwdOut];
   for (size_t i = 0; i < outputs.size(); ++i) {
     VarBase* out = outputs[i];
     out->stop_gradient_ = stop_gradient;
     out->pre_op_ = op;
-    out->pre_op_out_name_ = "Out";
+    out->pre_op_out_name_ = PyLayer::kFwdOut;
     out->pre_op_out_idx_ = i;
   }
   if (!stop_gradient) {
-    auto& grad_input_vars = op->grad_input_vars_["X@GRAD"];
-    auto& grad_output_vars = op->grad_output_vars_["Out@GRAD"];
+    auto& grad_input_vars =
+        op->grad_input_vars_[framework::GradVarName(PyLayer::kFwdInp)];
+    auto& grad_output_vars =
+        op->grad_output_vars_[framework::GradVarName(PyLayer::kFwdOut)];
 
     for (const VarBase* inp : inputs) {
       grad_input_vars.push_back(inp->var_);