add op activation improve for in/out diff (#548)

Former-commit-id: 7a8ce23c

oneflow/core/operator/clone_op.h

@@ -11,6 +11,8 @@ class CloneOp final : public Operator {
   CloneOp() = default;
   ~CloneOp() = default;
 
+  bool NeedExtraInDiffMemWhenBackward() const override { return false; }
+  bool NeedOutWhenBackward() const override { return false; }
   void InitFromOpConf() override;
   const PbMessage& GetSpecialConf() const override;
   void InferBlobDescs(

oneflow/core/operator/concat_op.h

@@ -11,6 +11,8 @@ class ConcatOp final : public Operator {
   ConcatOp() = default;
   ~ConcatOp() = default;
 
+  bool NeedExtraInDiffMemWhenBackward() const override { return false; }
+  bool NeedOutWhenBackward() const override { return false; }
   void InitFromOpConf() override;
 
   const PbMessage& GetSpecialConf() const override;

oneflow/core/operator/softmax_op.h

@@ -11,6 +11,7 @@ class SoftmaxOp final : public Operator {
   SoftmaxOp() = default;
   ~SoftmaxOp() = default;
 
+  bool NeedExtraInDiffMemWhenBackward() const override { return false; }
   void InitFromOpConf() override;
   const PbMessage& GetSpecialConf() const override;