[jit] add jit layer function default constructor (#45169)

* fix jit layer function

* fix comment

* fix comment

paddle/fluid/jit/function.cc

@@ -30,12 +30,20 @@ Function::Function(BaseEngine* engine) : engine_(engine) {}
 
 std::vector<Tensor> Function::operator()(
     const std::vector<Tensor>& inputs) const {
+  PADDLE_ENFORCE_EQ(IsValid(),
+                    true,
+                    phi::errors::PreconditionNotMet(
+                        "Funtion engine ptr is nullptr, please check it."));
   auto dense_tensors = utils::ToDenseTensors(inputs);
   return utils::ToTensors(this->operator()(dense_tensors));
 }
 
 std::vector<DenseTensor> Function::operator()(
     const std::vector<DenseTensor>& inputs) const {
+  PADDLE_ENFORCE_EQ(IsValid(),
+                    true,
+                    phi::errors::PreconditionNotMet(
+                        "Funtion engine ptr is nullptr, please check it."));
   return (*engine_)(inputs);
 }
 

paddle/fluid/jit/function.h

@@ -27,6 +27,7 @@ using Tensor = paddle::experimental::Tensor;
 
 class Function {
  public:
+  Function() : engine_(nullptr) {}
   explicit Function(BaseEngine* engine);
 
   std::vector<Tensor> operator()(const std::vector<Tensor>& inputs) const;
@@ -34,6 +35,8 @@ class Function {
   std::vector<DenseTensor> operator()(
       const std::vector<DenseTensor>& inputs) const;
 
+  bool IsValid() const { return engine_ != nullptr; }
+
   ~Function() = default;
 
  private:

paddle/fluid/jit/layer_test.cc

@@ -69,6 +69,11 @@ std::vector<Tensor> PrepareInputs(const phi::Place& place) {
   return utils::ToTensors({t});
 }
 
+TEST(CpuLayerTest, Function) {
+  auto func_null = Function();
+  EXPECT_TRUE(!func_null.IsValid());
+}
+
 TEST(CpuLayerTest, Construct) {
   auto place = phi::CPUPlace();
   std::string path = "./multi_program_load/export";
@@ -103,6 +108,7 @@ TEST(CpuLayerTest, Construct) {
   EXPECT_NEAR(out_data[0], 0.02194316, 1e-6);
 
   auto func = layer.Function("infer");
+  EXPECT_TRUE(func.IsValid());
   outs = func(inputs);
   out_data = outs[0].data<float>();
   EXPECT_NEAR(out_data[0], 1.41562390, 1e-6);
@@ -128,6 +134,7 @@ TEST(GpuLayerTest, Construct) {
   EXPECT_NEAR(out_data[0], 0.02194316, 1e-6);
 
   auto func = layer.Function("infer");
+  EXPECT_TRUE(func.IsValid());
   outs = func(inputs);
   gpu_tensor = outs[0];
   cpu_tensor = paddle::experimental::copy_to(gpu_tensor, phi::CPUPlace(), true);