[quant] Refactor qembeddingbag to remove duplicate code

aten/src/ATen/native/quantized/cpu/qembeddingbag.cpp

@@ -197,9 +197,9 @@ at::Tensor embedding_bag_4bit_helper(
 #endif
   return output;
 }
-} // namespace
 
-at::Tensor PackedEmbeddingBagWeight::embeddingbag_byte(
+at::Tensor embedding_bag_byte_helper(
+    const at::Tensor& packed_w,
     const at::Tensor& indices,
     const c10::optional<at::Tensor>& offsets_in,
     bool sparse,
@@ -297,6 +297,23 @@ at::Tensor PackedEmbeddingBagWeight::embeddingbag_byte(
   return output;
 }
 
+} // namespace
+
+at::Tensor PackedEmbeddingBagWeight::embeddingbag_byte(
+    const at::Tensor& indices,
+    const c10::optional<at::Tensor>& offsets_in,
+    bool sparse,
+    const c10::optional<at::Tensor>& per_sample_weights_,
+    bool include_last_offset) {
+  return embedding_bag_byte_helper(
+      packed_w,
+      indices,
+      offsets_in,
+      sparse,
+      per_sample_weights_,
+      include_last_offset);
+}
+
 at::Tensor PackedEmbeddingBagWeight::embeddingbag_4bit(
     const at::Tensor& indices,
     const c10::optional<at::Tensor>& offsets_in,
@@ -324,99 +341,18 @@ Tensor embedding_bag_byte_rowwise_offsets(
     const c10::optional<Tensor>& offsets_in,
     const bool /* scale_grad_by_freq */,
     const int64_t /* mode */,
-    bool /* sparse */,
+    bool sparse,
     const c10::optional<Tensor>& per_sample_weights_,
     bool include_last_offset) {
   TORCH_CHECK(weight.scalar_type() == at::kByte);
   TORCH_CHECK(weight.ndimension() == 2);
-  TORCH_CHECK(
-      offsets_in.has_value(),
-      "embedding_bag_byte_rowwise_offsets expects offsets to be set");
-
-  auto offsets = offsets_in.value();
-  auto offsets_data = offsets.data_ptr<int64_t>();
-  const auto weight_data = weight.data_ptr<uint8_t>();
-  const auto indices_data = indices.data_ptr<int64_t>();
-
-  const int64_t N = weight.size(0);
-  const int64_t D = weight.size(1) - 8; // NB: -8 to account for scale and bias
-  const int64_t M = offsets.size(0);
-
-  int64_t output_size = M - 1;
-  std::vector<int64_t> offsets_include_last;
-
-  if (!include_last_offset) {
-    output_size = M;
-    offsets_include_last.resize(M + 1);
-    std::memcpy(
-        offsets_include_last.data(),
-        offsets.data_ptr<int64_t>(),
-        sizeof(int64_t) * M);
-    offsets_include_last[M] = indices.numel();
-    offsets_data = offsets_include_last.data();
-  }
-
-  std::vector<int64_t> shape = {output_size, D};
-  auto output = at::empty(shape, weight.options().dtype(at::kFloat));
-  auto* output_data = output.data_ptr<float>();
-
-#ifdef USE_FBGEMM
-
-  auto kernel_i8_i64 =
-      fbgemm::GenerateEmbeddingSpMDM<uint8_t, int64_t, int64_t>(
-          /*block_size=*/D,
-          /*has_weight=*/per_sample_weights_.has_value(),
-          /*normalize_by_lengths=*/false,
-          /*prefetch=*/16, // NOLINT(cppcoreguidelines-avoid-magic-numbers)
-          /*is_weight_positional=*/false,
-          /*use_offsets=*/true);
-
-  if (weight.is_contiguous()) {
-    at::parallel_for(
-        0, output_size, 1, [&](int64_t start_idx, int64_t end_idx) {
-          bool success = kernel_i8_i64(
-              /*output_size=*/end_idx - start_idx,
-              /*index_size=*/offsets_data[end_idx] - offsets_data[start_idx],
-              /*data_size=*/N,
-              /*input=*/weight_data,
-              /*indices=*/indices_data + offsets_data[start_idx],
-              /*offsets_or_lengths=*/offsets_data + start_idx,
-              /*weights=*/
-              per_sample_weights_
-                  ? per_sample_weights_.value().data_ptr<float>() +
-                      offsets_data[start_idx]
-                  : nullptr,
-              /*out=*/output_data + start_idx * D);
-
-          TORCH_CHECK(
-              success,
-              "FBGEMM GenerateEmbeddingSpMDM kernel failed for 8-bit input");
-        });
-  } else {
-    auto weight_contig = weight.contiguous();
-    const auto weight_data_contig = weight_contig.data_ptr<uint8_t>();
-    at::parallel_for(
-        0, output_size, 1, [&](int64_t start_idx, int64_t end_idx) {
-          bool success = kernel_i8_i64(
-              /*output_size=*/end_idx - start_idx,
-              /*index_size=*/offsets_data[end_idx] - offsets_data[start_idx],
-              /*data_size=*/N,
-              /*input=*/weight_data_contig,
-              /*indices=*/indices_data + offsets_data[start_idx],
-              /*offsets_or_lengths=*/offsets_data + start_idx,
-              /*weights=*/
-              per_sample_weights_
-                  ? per_sample_weights_.value().data_ptr<float>() +
-                      offsets_data[start_idx]
-                  : nullptr,
-              /*out=*/output_data + start_idx * D);
-          TORCH_CHECK(
-              success,
-              "FBGEMM GenerateEmbeddingSpMDM kernel failed for 8-bit input");
-        });
-  }
-#endif
-  return output;
+  return embedding_bag_byte_helper(
+      weight,
+      indices,
+      offsets_in,
+      sparse,
+      per_sample_weights_,
+      include_last_offset);
 }
 
 Tensor embedding_bag_4bit_rowwise_offsets(