Merge pull request #7943 from pkuyym/fix-7939

Bug fix for sequence_reshape operator.

paddle/operators/sequence_reshape_op.cc

@@ -30,8 +30,13 @@ class SequenceReshapeOp : public framework::OperatorWithKernel {
     auto x_numel = product(x_dims);
     PADDLE_ENFORCE_EQ(x_dims.size(), 2U, "Rank of Input(X) should be 2.");
     int new_dim = ctx->Attrs().Get<int>("new_dim");
-    ctx->SetOutputDim("Out",
-                      {x_numel / new_dim, static_cast<int64_t>(new_dim)});
+    if (ctx->IsRuntime()) {
+      ctx->SetOutputDim("Out",
+                        {x_numel / new_dim, static_cast<int64_t>(new_dim)});
+    } else {
+      // when compiling, the batch size is undetermined, just set to -1
+      ctx->SetOutputDim("Out", {-1, static_cast<int64_t>(new_dim)});
+    }
   }
 };