Make operator Input/Output can return nullptr

paddle/framework/operator.cc

@@ -33,12 +33,18 @@ ExecutionContext::GetEigenDevice<platform::GPUPlace, Eigen::GpuDevice>() const {
 }
 #endif
 
-const std::string& OperatorBase::Input(const std::string& name) const {
+std::string OperatorBase::Input(const std::string& name) const {
   auto& ins = Inputs(name);
-  PADDLE_ENFORCE_EQ(ins.size(), 1UL,
-                    "Op %s input %s should contain only one variable", type_,
-                    name);
-  return ins[0];
+  switch (ins.size()) {
+    case 0:
+      return kEmptyVarName;
+    case 1:
+      return ins[0];
+    default:
+      PADDLE_THROW("Op %s input %s should contain only one variable", type_,
+                   name);
+      return "";
+  }
 }
 
 const std::vector<std::string>& OperatorBase::Inputs(
@@ -49,12 +55,18 @@ const std::vector<std::string>& OperatorBase::Inputs(
   return it->second;
 }
 
-const std::string& OperatorBase::Output(const std::string& name) const {
+std::string OperatorBase::Output(const std::string& name) const {
   auto& outs = Outputs(name);
-  PADDLE_ENFORCE_EQ(outs.size(), 1UL,
-                    "Op %s output %s should contain only one variable", type_,
-                    name);
-  return outs[0];
+  switch (outs.size()) {
+    case 0:
+      return kEmptyVarName;
+    case 1:
+      return outs[0];
+    default:
+      PADDLE_THROW("Op %s output %s should contain only one variable", type_,
+                   name);
+      return "";
+  }
 }
 
 const std::vector<std::string>& OperatorBase::Outputs(

paddle/framework/operator.h

@@ -95,12 +95,12 @@ class OperatorBase {
   const VariableNameMap& Inputs() const { return inputs_; }
   const VariableNameMap& Outputs() const { return outputs_; }
   //! Get a input with argument's name described in `op_proto`
-  const std::string& Input(const std::string& name) const;
+  std::string Input(const std::string& name) const;
   //! Get a input which has multiple variables.
   const std::vector<std::string>& Inputs(const std::string& name) const;
 
   //! Get a output with argument's name described in `op_proto`
-  const std::string& Output(const std::string& name) const;
+  std::string Output(const std::string& name) const;
   //! Get an output which has multiple variables.
   //! TODO add a vector_view to prevent memory copy.
   const std::vector<std::string>& Outputs(const std::string& name) const;
@@ -238,11 +238,21 @@ class InferShapeContext {
   }
 
   const Variable* InputVar(const std::string& name) const {
-    return scope_.FindVar(op_.Input(name));
+    auto ipt = op_.Input(name);
+    if (ipt == kEmptyVarName) {
+      return nullptr;
+    } else {
+      return scope_.FindVar(ipt);
+    }
   }
 
   Variable* OutputVar(const std::string& name) const {
-    return scope_.FindVar(op_.Output(name));
+    auto opt = op_.Output(name);
+    if (opt == kEmptyVarName) {
+      return nullptr;
+    } else {
+      return scope_.FindVar(opt);
+    }
   }
 
   const std::vector<const Variable*> MultiInputVar(
@@ -250,9 +260,11 @@ class InferShapeContext {
     auto names = op_.Inputs(name);
     std::vector<const Variable*> res;
     res.reserve(names.size());
-    std::transform(
-        names.begin(), names.end(), std::back_inserter(res),
-        [this](const std::string& name) { return scope_.FindVar(name); });
+    std::transform(names.begin(), names.end(), std::back_inserter(res),
+                   [this](const std::string& name) {
+                     return name != kEmptyVarName ? scope_.FindVar(name)
+                                                  : nullptr;
+                   });
     return res;
   }
 
@@ -260,24 +272,24 @@ class InferShapeContext {
     auto names = op_.Outputs(name);
     std::vector<const Variable*> res;
     res.reserve(names.size());
-    std::transform(
-        names.begin(), names.end(), std::back_inserter(res),
-        [this](const std::string& name) { return scope_.FindVar(name); });
+    std::transform(names.begin(), names.end(), std::back_inserter(res),
+                   [this](const std::string& name) {
+                     return name != kEmptyVarName ? scope_.FindVar(name)
+                                                  : nullptr;
+                   });
     return res;
   }
 
   template <typename T>
   const T* Input(const std::string& name) const {
     auto* var = InputVar(name);
-    PADDLE_ENFORCE_NOT_NULL(var, "Input(%s) should not be nullptr", name);
-    return &var->Get<T>();
+    return var == nullptr ? nullptr : &var->Get<T>();
   }
 
   template <typename T>
   T* Output(const std::string& name) const {
     auto var = OutputVar(name);
-    PADDLE_ENFORCE_NOT_NULL(var, "Output(%s) should not be nullptr", name);
-    return var->GetMutable<T>();
+    return var == nullptr ? nullptr : var->GetMutable<T>();
   }
 
   template <typename T>
@@ -288,10 +300,7 @@ class InferShapeContext {
     std::transform(names.begin(), names.end(), std::back_inserter(res),
                    [&](const std::string& sub_name) {
                      auto var = scope_.FindVar(sub_name);
-                     PADDLE_ENFORCE_NOT_NULL(
-                         var, "MultiInput(%s:%s) should not be nullptr", name,
-                         sub_name);
-                     return &var->Get<T>();
+                     return var == nullptr ? nullptr : &var->Get<T>();
                    });
     return res;
   }
@@ -304,10 +313,7 @@ class InferShapeContext {
     std::transform(names.begin(), names.end(), std::back_inserter(res),
                    [&](const std::string& sub_name) {
                      auto var = scope_.FindVar(sub_name);
-                     PADDLE_ENFORCE_NOT_NULL(
-                         var, "MultiOutput(%s:%s) should not be nullptr.", name,
-                         sub_name);
-                     return var->GetMutable<T>();
+                     return var == nullptr ? nullptr : var->GetMutable<T>();
                    });
     return res;
   }