forward and backward

test=develop

paddle/fluid/imperative/layer.cc

@@ -57,6 +57,7 @@ class Autograd {
     if (var->stop_gradient_) {
       return;
     }
+    VLOG(3) << "start autograd";
 
     std::deque<OpBase*> ready;
     ready.push_back(var->pre_op_);
@@ -122,11 +123,10 @@ framework::LoDTensor& VarBase::Grad() {
 }
 
 std::map<std::string, std::vector<VarBase*>> OpBase::ApplyGrad() {
-  if (!grad_op_desc_) {
+  if (!grad_op_desc_ && backward_id_ <= 0) {
     LOG(WARNING) << "op with no grad: " << op_desc_->Type();
     return {};
   }
-  VLOG(3) << "op grad " << grad_op_desc_->Type();
 
   std::vector<std::unique_ptr<framework::Variable>> tmp_vars;
   std::map<std::string, std::vector<framework::Variable*>> grad_outputs;
@@ -142,6 +142,12 @@ std::map<std::string, std::vector<VarBase*>> OpBase::ApplyGrad() {
     }
   }
 
+  if (backward_id_ > 0) {
+    VLOG(3) << "py_layer_grad";
+    PyLayer::ApplyGrad(backward_id_, grad_input_vars_["X@GRAD"],
+                       &(grad_outputs["Out@GRAD"]));
+  } else {
+    VLOG(3) << "op grad " << grad_op_desc_->Type();
     framework::RuntimeContext ctx(grad_input_vars_, grad_outputs);
 
     // No need to do compile time infer shape here.
@@ -159,6 +165,7 @@ std::map<std::string, std::vector<VarBase*>> OpBase::ApplyGrad() {
     PreparedOp p = PreparedOp::Prepare(ctx, *op_kernel, place);
     p.op.RuntimeInferShape(scope, place, ctx);
     p.func(framework::ExecutionContext(p.op, scope, *p.dev_ctx, p.ctx));
+  }
 
   for (auto it : grad_output_vars_) {
     auto& outputs = grad_outputs[it.first];
@@ -175,6 +182,7 @@ std::map<std::string, std::vector<VarBase*>> OpBase::ApplyGrad() {
 void VarBase::RunBackward() {
   if (!pre_op_) return;
 
+  VLOG(3) << "start backward";
   auto grads_t = grads_->GetMutable<framework::LoDTensor>();
   float* data = grads_t->mutable_data<float>(platform::CPUPlace());
   std::fill(data, data + grads_t->numel(), 1.0);
@@ -190,17 +198,30 @@ void PyLayer::RegisterFunc(int func_id, const py::object& py_func) {
 }
 
 std::vector<VarBase*> PyLayer::Apply(int func_id,
-                                     const std::vector<VarBase>& inputs) {
+                                     const std::vector<VarBase*>& inputs) {
   std::vector<framework::LoDTensor> tensor_inputs;
   std::vector<VarBase*> ret;
 
-  for (const VarBase& in : inputs) {
-    tensor_inputs.push_back(in.var_->Get<framework::LoDTensor>());
+  for (const VarBase* in : inputs) {
+    tensor_inputs.push_back(in->var_->Get<framework::LoDTensor>());
   }
   PADDLE_ENFORCE(py_funcs_.find(func_id) != py_funcs_.end());
   CallPythonFunc(py_funcs_[func_id], tensor_inputs, &ret);
   return ret;
 }
 
+void PyLayer::ApplyGrad(int func_id,
+                        const std::vector<framework::Variable*>& inputs,
+                        std::vector<framework::Variable*>* outputs) {
+  std::vector<framework::LoDTensor> tensor_inputs;
+  std::vector<VarBase*> ret;
+
+  for (const Variable* in : inputs) {
+    tensor_inputs.push_back(in->Get<framework::LoDTensor>());
+  }
+  PADDLE_ENFORCE(py_funcs_.find(func_id) != py_funcs_.end());
+  CallPythonFunc(py_funcs_[func_id], tensor_inputs, outputs);
+}
+
 }  // namespace imperative
 }  // namespace paddle

paddle/fluid/imperative/layer.h

@@ -196,6 +196,35 @@ static void CallPythonFunc(const py::object& callable,
   }
 }
 
+static void CallPythonFunc(const py::object& callable,
+                           const std::vector<framework::LoDTensor>& ins,
+                           std::vector<framework::Variable*>* outs) {
+  py::gil_scoped_acquire guard;
+  py::tuple in_args(ins.size());
+  for (size_t i = 0; i < ins.size(); ++i) {
+    in_args[i] = ins[i].IsInitialized() ? py::cast(ins[i]) : py::cast(nullptr);
+  }
+  VLOG(3) << "pyfunc in " << py::len(in_args);
+
+  // TODO(panyx0718): Who owns the returned LoDTensor.
+  auto ret = callable(in_args);
+  auto ret_tuple = py::cast<py::tuple>(ret);
+  size_t ret_num = py::len(ret_tuple);
+  VLOG(3) << "pyfunc out " << ret_num;
+  for (size_t i = 0; i < ret_num; ++i) {
+    try {
+      auto* py_out_tensor = py::cast<framework::LoDTensor*>(ret_tuple[i]);
+      PADDLE_ENFORCE_NOT_NULL(py_out_tensor,
+                              "Output tensor %d should not be nullptr", i);
+      auto* tensor = (*outs)[i]->GetMutable<framework::LoDTensor>();
+      tensor->ShareDataWith(*py_out_tensor);
+      tensor->set_lod(py_out_tensor->lod());
+    } catch (py::cast_error&) {
+      PADDLE_THROW("The %d-th output must be LoDTensor", i);
+    }
+  }
+}
+
 class PyLayer {
  public:
   virtual ~PyLayer() {}
@@ -203,7 +232,11 @@ class PyLayer {
   static void RegisterFunc(int func_id, const py::object& py_func);
 
   static std::vector<VarBase*> Apply(int func_id,
-                                     const std::vector<VarBase>& inputs);
+                                     const std::vector<VarBase*>& inputs);
+
+  static void ApplyGrad(int func_id,
+                        const std::vector<framework::Variable*>& inputs,
+                        std::vector<framework::Variable*>* outputs);
 };
 
 }  // namespace imperative

paddle/fluid/imperative/tracer.h

@@ -131,6 +131,7 @@ class Tracer {
 
     if (!stop_gradient) {
       framework::OpDesc* grad_op_desc;
+      // TODO(panyx): Is this leaked?
       auto grad_to_var = new std::unordered_map<std::string, std::string>();
       CreateGradOp(*op_desc, {}, {block}, &grad_op_desc, grad_to_var);
       op->grad_op_desc_ = grad_op_desc;
@@ -143,12 +144,14 @@ class Tracer {
           if (var_it == grad_to_var->end()) {
             auto fwd_var_it = vars.find(grad_invar);
             PADDLE_ENFORCE(fwd_var_it != vars.end());
+            // Forward inputs or outputs.
             grad_in_vars.push_back(fwd_var_it->second->var_);
           } else {
             VarBase* var = vars[var_it->second];
             if (!var->grads_->IsInitialized()) {
               InitVar(var->var_, var->grads_);
             }
+            // Douts.
             grad_in_vars.push_back(var->grads_);
           }
         }
@@ -172,18 +175,51 @@ class Tracer {
     op->block_ = block;
   }
 
-  std::vector<VarBase*> PyTrace(OpBase* op,
-                                const std::vector<VarBase>& inputs) {
-    std::vector<VarBase*> outputs = PyLayer::Apply(op->forward_id_, inputs);
-    /*
-    for (const VarBase& inp : inputs) {
-      if (inp.pre_op_) {
-        op->pre_ops_[it.first].push_back(inp->pre_op_);
-        op->pre_ops_out_idx_[it.first].push_back(inp->pre_op_out_idx_);
+  std::vector<VarBase*> PyTrace(OpBase* op, const std::vector<VarBase*>& inputs,
+                                bool stop_gradient = false) {
+    VLOG(3) << "py_trace";
+    op->input_vars_["X"] = inputs;
+    op->output_vars_["Out"] = 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_);
       } else {
-        op->pre_ops_[it.first].push_back(nullptr);
+        op->pre_ops_["X"].push_back(nullptr);
+      }
+    }
+
+    auto& outputs = op->output_vars_["Out"];
+    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_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"];
+
+      for (const VarBase* inp : inputs) {
+        grad_input_vars.push_back(inp->var_);
+      }
+      for (VarBase* out : outputs) {
+        grad_input_vars.push_back(out->var_);
+      }
+      for (VarBase* out : outputs) {
+        grad_input_vars.push_back(out->grads_);
+        if (!grad_input_vars.back()->IsInitialized()) {
+          InitVar(out->var_, grad_input_vars.back());
+        }
+      }
+      for (const VarBase* inp : inputs) {
+        grad_output_vars.push_back(inp->grads_);
+        if (!grad_output_vars.back()->IsInitialized()) {
+          InitVar(inp->var_, grad_output_vars.back());
+        }
+      }
     }
-    }*/
     return outputs;
   }
 

paddle/fluid/pybind/pybind.cc

@@ -175,6 +175,13 @@ PYBIND11_MODULE(core, m) {
           [](imperative::OpBase &self, int forward_id) {
             self.forward_id_ = forward_id;
           },
+          py::return_value_policy::reference)
+      .def_property(
+          "backward_id",
+          [](const imperative::OpBase &self) { return self.backward_id_; },
+          [](imperative::OpBase &self, int backward_id) {
+            self.backward_id_ = backward_id;
+          },
           py::return_value_policy::reference);
 
   py::class_<imperative::Layer, Layer /* <--- trampoline*/> layer(m, "Layer");
@@ -188,7 +195,7 @@ PYBIND11_MODULE(core, m) {
       .def(py::init<>())
       .def_static(
           "apply",
-          [](int func_id, const std::vector<imperative::VarBase> &inputs)
+          [](int func_id, const std::vector<imperative::VarBase *> &inputs)
               -> std::vector<imperative::VarBase *> {
                 return imperative::PyLayer::Apply(func_id, inputs);
               },

python/paddle/fluid/imperative/layers.py

@@ -59,22 +59,23 @@ class PyLayer(core.PyLayer):
         raise NotImplementedError
 
     @staticmethod
-    def backward(inputs):
+    def backward(douts):
         raise NotImplementedError
 
     @classmethod
     def __call__(cls, inputs):
         tracer = framework._imperative_tracer()
         block = framework.default_main_program().current_block()
-        inputs = map(base.to_variable, inputs)
         inputs = [x._ivar for x in inputs]
 
         PyLayer.register_func(1, cls.forward)
+        PyLayer.register_func(2, cls.backward)
 
         iop = core.OpBase()
         iop.forward_id = 1
+        iop.backward_id = 2
         block.ops.append(iop)
-        ivars = tracer.py_trace(iop, inputs)
+        ivars = tracer.py_trace(iop, inputs, False)
         # ivars = core.PyLayer.apply(cls.forward, inputs)
         ret = []
         for ivar in ivars:

python/paddle/fluid/tests/unittests/test_imperative.py

@@ -49,8 +49,18 @@ class MyPyLayer(fluid.imperative.PyLayer):
         return tuple([tensor])
 
     @staticmethod
-    def backward(douts, outs):
-        return np.array(douts[0]) * (1 - np.square(np.array(outs[0])))
+    def backward(inputs):
+        sys.stderr.write('calling into backward: %s\n' % str(inputs))
+        inp, out, dout = inputs
+        inp = np.array(inp)
+        out = np.array(out)
+        dout = np.array(dout)
+        sys.stderr.write('calling into backward: %s, %s, %s\n' %
+                         (inp, out, dout))
+        ret = np.array(dout) * (1 - np.square(np.array(out)))
+        tensor = core.LoDTensor()
+        tensor.set(ret, core.CPUPlace())
+        return tuple([tensor])
 
 
 class MLP(fluid.imperative.Layer):
@@ -71,20 +81,44 @@ class MLP(fluid.imperative.Layer):
 
 
 class TestImperative(unittest.TestCase):
+    """
     def test_layer(self):
         with fluid.imperative.guard():
             cl = core.Layer()
             cl.forward([])
             l = fluid.imperative.Layer()
             self.assertRaises(NotImplementedError, l.forward, [])
+    """
 
     def test_pylayer(self):
+        np_inp = np.ones([2, 2], np.float32)
         with fluid.imperative.guard():
             my_py_layer = MyPyLayer()
-            outs = my_py_layer([np.ones([2, 2], np.float32)])
-            sys.stderr.write('%s\n' % outs[0]._numpy())
-            # out.backward()
+            var_inp = fluid.imperative.base.to_variable(np_inp)
+            outs = my_py_layer([var_inp])
+            dy_out = np.sum(outs[0]._numpy())
+            outs[0]._backward()
+            dy_grad = var_inp._gradient()
+
+        with new_program_scope():
+            inp = fluid.layers.data(
+                name="inp", shape=[2, 2], append_batch_size=False)
+            # TODO(panyx0718): Paddle doesn't diff against data `inp`.
+            x1 = inp * 1
+            # TODO(panyx0718): If reduce_sum is skipped, the result is wrong.
+            x = fluid.layers.reduce_sum(fluid.layers.tanh(x1))
+            param_grads = fluid.backward.append_backward(
+                x, parameter_list=[x1.name])[0]
+            exe = fluid.Executor(fluid.CPUPlace())
+
+            static_out, static_grad = exe.run(
+                feed={inp.name: np_inp},
+                fetch_list=[x.name, param_grads[1].name])
+
+        self.assertTrue(np.allclose(dy_out, static_out))
+        self.assertTrue(np.allclose(dy_grad, static_grad))
 
+    """
     def test_layer_in_out(self):
         np_inp = np.array([1.0, 2.0, -1.0], dtype=np.float32)
         with fluid.imperative.guard():
@@ -138,6 +172,7 @@ class TestImperative(unittest.TestCase):
 
         self.assertTrue(np.allclose(dy_out, static_out))
         self.assertTrue(np.allclose(dy_grad, static_grad))
+    """
 
 
 if __name__ == '__main__':