Fix sequence_pool_op in debug mode

The rank of the tensor from the chip() function is changed. In release mode, eigen_assert is not enabled and the dimenstion mismatch is not detected.

Author: xuwei06

paddle/operators/sequence_pool_op.h

@@ -126,6 +126,7 @@ class SequencePoolGradKernel : public framework::OpKernel<T> {
       int64_t h = static_cast<int64_t>(lod[i + 1] - lod[i]);
       auto in_g_e = EigenMatrix<T>::From(in_g_t, {h, w});
       auto out_g_e = EigenMatrix<T>::From(out_g_t, {1, w});
+      auto out_g_e_v = EigenVector<T>::Flatten(out_g_t);
       Eigen::DSizes<int, 2> bcast(h, 1);
 
       if (pooltype == "AVERAGE") {
@@ -136,9 +137,9 @@ class SequencePoolGradKernel : public framework::OpKernel<T> {
         in_g_e.device(place) =
             (out_g_e / std::sqrt(static_cast<T>(h))).broadcast(bcast);
       } else if (pooltype == "LAST") {
-        in_g_e.chip(h - 1, 0).device(place) = out_g_e;
+        in_g_e.chip(h - 1, 0).device(place) = out_g_e_v;
       } else if (pooltype == "FIRST") {
-        in_g_e.chip(0, 0).device(place) = out_g_e;
+        in_g_e.chip(0, 0).device(place) = out_g_e_v;
       } else {
         PADDLE_THROW("unsupported pooling pooltype");
       }