[R-package] Fix inefficiency in retrieving pointers (#6208)

Author: david-cortes

Diff for: R-package/src/lightgbm_R.cpp

@@ -226,9 +226,10 @@ SEXP LGBM_DatasetGetSubset_R(SEXP handle,
   int32_t len = static_cast<int32_t>(Rf_asInteger(len_used_row_indices));
   std::vector<int32_t> idxvec(len);
   // convert from one-based to zero-based index
+  const int *used_row_indices_ = INTEGER(used_row_indices);
 #pragma omp parallel for num_threads(OMP_NUM_THREADS()) schedule(static, 512) if (len >= 1024)
   for (int32_t i = 0; i < len; ++i) {
-    idxvec[i] = static_cast<int32_t>(INTEGER(used_row_indices)[i] - 1);
+    idxvec[i] = static_cast<int32_t>(used_row_indices_[i] - 1);
   }
   const char* parameters_ptr = CHAR(PROTECT(Rf_asChar(parameters)));
   DatasetHandle res = nullptr;
@@ -339,18 +340,20 @@ SEXP LGBM_DatasetSetField_R(SEXP handle,
   const char* name = CHAR(PROTECT(Rf_asChar(field_name)));
   if (!strcmp("group", name) || !strcmp("query", name)) {
     std::vector<int32_t> vec(len);
+    const int *field_data_ = INTEGER(field_data);
 #pragma omp parallel for num_threads(OMP_NUM_THREADS()) schedule(static, 512) if (len >= 1024)
     for (int i = 0; i < len; ++i) {
-      vec[i] = static_cast<int32_t>(INTEGER(field_data)[i]);
+      vec[i] = static_cast<int32_t>(field_data_[i]);
     }
     CHECK_CALL(LGBM_DatasetSetField(R_ExternalPtrAddr(handle), name, vec.data(), len, C_API_DTYPE_INT32));
   } else if (!strcmp("init_score", name)) {
     CHECK_CALL(LGBM_DatasetSetField(R_ExternalPtrAddr(handle), name, REAL(field_data), len, C_API_DTYPE_FLOAT64));
   } else {
     std::vector<float> vec(len);
+    const double *field_data_ = REAL(field_data);
 #pragma omp parallel for num_threads(OMP_NUM_THREADS()) schedule(static, 512) if (len >= 1024)
     for (int i = 0; i < len; ++i) {
-      vec[i] = static_cast<float>(REAL(field_data)[i]);
+      vec[i] = static_cast<float>(field_data_[i]);
     }
     CHECK_CALL(LGBM_DatasetSetField(R_ExternalPtrAddr(handle), name, vec.data(), len, C_API_DTYPE_FLOAT32));
   }
@@ -372,21 +375,24 @@ SEXP LGBM_DatasetGetField_R(SEXP handle,
   if (!strcmp("group", name) || !strcmp("query", name)) {
     auto p_data = reinterpret_cast<const int32_t*>(res);
     // convert from boundaries to size
+    int *field_data_ = INTEGER(field_data);
 #pragma omp parallel for num_threads(OMP_NUM_THREADS()) schedule(static, 512) if (out_len >= 1024)
     for (int i = 0; i < out_len - 1; ++i) {
-      INTEGER(field_data)[i] = p_data[i + 1] - p_data[i];
+      field_data_[i] = p_data[i + 1] - p_data[i];
     }
   } else if (!strcmp("init_score", name)) {
     auto p_data = reinterpret_cast<const double*>(res);
+    double *field_data_ = REAL(field_data);
 #pragma omp parallel for num_threads(OMP_NUM_THREADS()) schedule(static, 512) if (out_len >= 1024)
     for (int i = 0; i < out_len; ++i) {
-      REAL(field_data)[i] = p_data[i];
+      field_data_[i] = p_data[i];
     }
   } else {
     auto p_data = reinterpret_cast<const float*>(res);
+    double *field_data_ = REAL(field_data);
 #pragma omp parallel for num_threads(OMP_NUM_THREADS()) schedule(static, 512) if (out_len >= 1024)
     for (int i = 0; i < out_len; ++i) {
-      REAL(field_data)[i] = p_data[i];
+      field_data_[i] = p_data[i];
     }
   }
   UNPROTECT(1);
@@ -611,10 +617,12 @@ SEXP LGBM_BoosterUpdateOneIterCustom_R(SEXP handle,
   int is_finished = 0;
   int int_len = Rf_asInteger(len);
   std::vector<float> tgrad(int_len), thess(int_len);
+  const double *grad_ = REAL(grad);
+  const double *hess_ = REAL(hess);
 #pragma omp parallel for num_threads(OMP_NUM_THREADS()) schedule(static, 512) if (int_len >= 1024)
   for (int j = 0; j < int_len; ++j) {
-    tgrad[j] = static_cast<float>(REAL(grad)[j]);
-    thess[j] = static_cast<float>(REAL(hess)[j]);
+    tgrad[j] = static_cast<float>(grad_[j]);
+    thess[j] = static_cast<float>(hess_[j]);
   }
   CHECK_CALL(LGBM_BoosterUpdateOneIterCustom(R_ExternalPtrAddr(handle), tgrad.data(), thess.data(), &is_finished));
   return R_NilValue;