Merge pull request #14720 from sneaxiy/fix_seq_mask_op_infershape

Fix sequence_mask_op InferShape

paddle/fluid/operators/sequence_ops/sequence_mask_op.h

@@ -36,13 +36,11 @@ class SequenceMaskOp : public framework::OperatorWithKernel {
     PADDLE_ENFORCE(ctx->HasInput("X"), "Input(X) must exist");
     PADDLE_ENFORCE(ctx->HasOutput("Y"), "Output(Y) must exist");
 
-    auto maxlen = ctx->Attrs().Get<int>("maxlen");
-    if (maxlen > 0) {  // We can only infershape when maxlen > 0
+    int maxlen = ctx->Attrs().Get<int>("maxlen");
     auto dim = framework::vectorize2int(ctx->GetInputDim("X"));
-      dim.push_back(maxlen);
+    dim.push_back(maxlen > 0 ? maxlen : -1);
     ctx->SetOutputDim("Y", framework::make_ddim(dim));
   }
-  }
 };
 
 class SequenceMaskOpMaker : public framework::OpProtoAndCheckerMaker {