Support stop_gradients var in imperative backward

test=develop

paddle/fluid/framework/operator.h

@@ -69,6 +69,15 @@ inline std::string GradVarName(const std::string& var_name) {
   return result;
 }
 
+inline std::string OriginVarName(const std::string& grad_var_name) {
+  std::size_t pos = grad_var_name.find_last_of(kGradVarSuffix);
+  if (pos == std::string::npos) {
+    return grad_var_name;
+  } else {
+    return grad_var_name.substr(0, pos);
+  }
+}
+
 proto::VarType::Type GetDataTypeOfVar(const Variable* var);
 const Tensor* GetLoDTensorOrSelectedRowsValueFromVar(const Variable& var);
 Tensor* GetMutableLoDTensorOrSelectedRowsValueFromVar(Variable* var);

paddle/fluid/framework/operator_test.cc

@@ -288,3 +288,12 @@ TEST(OpKernel, multi_inputs) {
   auto op = paddle::framework::OpRegistry::CreateOp(op_desc);
   op->Run(scope, cpu_place);
 }
+
+TEST(Functions, all) {
+  std::string var_name("X");
+  std::string grad_var_name = paddle::framework::GradVarName(var_name);
+  ASSERT_EQ(grad_var_name.c_str(), "X@GRAD");
+  std::string original_var_name =
+      paddle::framework::OriginVarName(grad_var_name);
+  ASSERT_EQ(original_var_name.c_str(), "X");
+}

paddle/fluid/imperative/layer.cc

@@ -21,6 +21,7 @@
 
 #include "paddle/fluid/framework/lod_tensor.h"
 #include "paddle/fluid/framework/op_registry.h"
+#include "paddle/fluid/framework/operator.h"
 #include "paddle/fluid/string/printf.h"
 
 namespace paddle {
@@ -31,8 +32,9 @@ using framework::Variable;
 void AddTo(Variable* src, Variable* dst) {
   framework::LoDTensor* dst_tensor = dst->GetMutable<framework::LoDTensor>();
   framework::LoDTensor* src_tensor = src->GetMutable<framework::LoDTensor>();
-  PADDLE_ENFORCE(dst_tensor->numel() == src_tensor->numel(), "%lld vs %lld",
-                 dst_tensor->numel(), src_tensor->numel());
+  PADDLE_ENFORCE(dst_tensor->numel() == src_tensor->numel(),
+                 "dst_numel %lld vs. src_numel %lld", dst_tensor->numel(),
+                 src_tensor->numel());
   float* dst_data = dst_tensor->mutable_data<float>(platform::CPUPlace());
   const float* src_data = src_tensor->data<float>();
   for (size_t i = 0; i < src_tensor->numel(); ++i) {
@@ -114,7 +116,7 @@ framework::LoDTensor& VarBase::Grad() {
 
 std::map<std::string, std::vector<VarBase*>> OpBase::ApplyGrad() {
   if (!grad_op_desc_) {
-    VLOG(3) << "op with no grad: " << op_desc_->Type();
+    LOG(WARNING) << "op with no grad: " << op_desc_->Type();
     return {};
   }
   VLOG(3) << "op grad " << grad_op_desc_->Type();
@@ -124,20 +126,18 @@ std::map<std::string, std::vector<VarBase*>> OpBase::ApplyGrad() {
   for (auto it : grad_output_vars_) {
     auto& outputs = grad_outputs[it.first];
     for (size_t i = 0; i < it.second.size(); ++i) {
-      tmp_vars.emplace_back(new framework::Variable());
-      outputs.push_back(tmp_vars.back().get());
-      outputs.back()->GetMutable<framework::LoDTensor>();
+      // Allocate a new variable
+      Variable* tmp_var = new framework::Variable();
+      tmp_var->GetMutable<framework::LoDTensor>();
+
+      tmp_vars.emplace_back(tmp_var);
+      outputs.push_back(tmp_var);
     }
-    grad_invar_desc.SetShape(
-        framework::vectorize(var->Get<framework::LoDTensor>().dims()));
-    VLOG(3)
-        << "set op grad var desc's shape size "
-        << framework::vectorize(var->Get<framework::LoDTensor>().dims()).size();
   }
 
   framework::RuntimeContext ctx(grad_input_vars_, grad_outputs);
 
-  // No need to do static infer shape here.
+  // No need to do compile time infer shape here.
   // grad_op_desc_->InferShape(*block_);
   grad_op_desc_->InferVarType(block_);
 
@@ -156,11 +156,16 @@ std::map<std::string, std::vector<VarBase*>> OpBase::ApplyGrad() {
   for (auto it : grad_output_vars_) {
     auto& outputs = grad_outputs[it.first];
     auto& origin_outputs = it.second;
+
+    auto& forward_inputs = input_vars_[framework::OriginVarName(it.first)];
+
     for (size_t i = 0; i < outputs.size(); ++i) {
+      if (!forward_inputs[i]->stop_gradient_) {
         framework::Variable* orig_grad = origin_outputs[i];
         AddTo(outputs[i], orig_grad);
       }
     }
+  }
   return input_vars_;
 }
 

paddle/fluid/imperative/tracer.h

@@ -57,7 +57,7 @@ class Tracer {
   void Trace(OpBase* op,
              const std::map<std::string, std::vector<VarBase*>>& inputs,
              const std::map<std::string, std::vector<VarBase*>>& outputs,
-             framework::BlockDesc* block) {
+             framework::BlockDesc* block, const bool stop_gradient) {
     std::map<std::string, VarBase*> vars;
 
     framework::OpDesc* op_desc = op->op_desc_;

paddle/fluid/pybind/pybind.cc

@@ -152,7 +152,7 @@ PYBIND11_MODULE(core, m) {
           [](const imperative::VarBase &self) { return self.stop_gradient_; },
           [](imperative::VarBase &self, bool stop_gradient) {
             self.stop_gradient_ = stop_gradient;
-          })
+          });
 
   py::class_<imperative::OpBase, PyOpBase>(m, "OpBase", R"DOC()DOC")
       .def(py::init<>())