Merge pull request #4918 from wanghaoshuang/fix_lod

Make LoDTensor::lod_element return start and end offset of sequence

paddle/framework/lod_tensor.h

@@ -74,12 +74,12 @@ class LoDTensor : public Tensor {
   LoD lod() const { return lod_; }
 
   /*
-   * Get a element from LoD.
+   * Get the start offset and end offset of an  element from LoD.
    */
-  size_t lod_element(size_t level, size_t elem) const {
+  std::pair<size_t, size_t> lod_element(size_t level, size_t elem) const {
     PADDLE_ENFORCE_LT(level, NumLevels());
     PADDLE_ENFORCE_LT(elem, NumElements(level));
-    return (lod_)[level][elem];
+    return std::make_pair((lod_)[level][elem], (lod_)[level][elem + 1]);
   }
 
   /*

paddle/framework/lod_tensor_test.cu

@@ -36,8 +36,8 @@ TEST(LoDTensor, LoDInGPU) {
   lod_tensor.mutable_data<float>(place);
 
   lod_tensor.set_lod(src_lod);
-  CHECK_EQ(lod_tensor.lod_element(0, 2), 4UL);
-  CHECK_EQ(lod_tensor.lod_element(0, 4), 8UL);
+  CHECK_EQ(lod_tensor.lod_element(0, 2).first, 4UL);
+  CHECK_EQ(lod_tensor.lod_element(0, 4).first, 8UL);
 
   auto lod = lod_tensor.lod();