[GPU-Plugin] Major refactor 2 (#2664)

* Change cmake option

* Move source files

* Move google tests

* Move python tests

* Move benchmarks

* Move documentation

* Remove makefile support

* Fix test run

* Move GPU tests

tests/cpp/predictor/test_gpu_predictor.cu

@@ -0,0 +1,73 @@
+
+/*!
+ * Copyright 2017 XGBoost contributors
+ */
+#include <xgboost/c_api.h>
+#include <xgboost/predictor.h>
+#include "gtest/gtest.h"
+#include "../helpers.h"
+
+namespace xgboost {
+namespace predictor {
+TEST(gpu_predictor, Test) {
+  std::unique_ptr<Predictor> gpu_predictor =
+      std::unique_ptr<Predictor>(Predictor::Create("gpu_predictor"));
+  std::unique_ptr<Predictor> cpu_predictor =
+      std::unique_ptr<Predictor>(Predictor::Create("cpu_predictor"));
+
+  std::vector<std::unique_ptr<RegTree>> trees;
+  trees.push_back(std::make_unique<RegTree>());
+  trees.back()->InitModel();
+  (*trees.back())[0].set_leaf(1.5f);
+  gbm::GBTreeModel model(0.5);
+  model.CommitModel(std::move(trees), 0);
+  model.param.num_output_group = 1;
+
+  int n_row = 5;
+  int n_col = 5;
+
+  auto dmat = CreateDMatrix(n_row, n_col, 0);
+
+  // Test predict batch
+  std::vector<float> gpu_out_predictions;
+  std::vector<float> cpu_out_predictions;
+  gpu_predictor->PredictBatch(dmat.get(), &gpu_out_predictions, model, 0);
+  cpu_predictor->PredictBatch(dmat.get(), &cpu_out_predictions, model, 0);
+  float abs_tolerance = 0.001;
+  for (int i = 0; i < gpu_out_predictions.size(); i++) {
+    ASSERT_LT(std::abs(gpu_out_predictions[i] - cpu_out_predictions[i]),
+              abs_tolerance);
+  }
+
+  // Test predict instance
+  auto batch = dmat->RowIterator()->Value();
+  for (int i = 0; i < batch.size; i++) {
+    std::vector<float> gpu_instance_out_predictions;
+    std::vector<float> cpu_instance_out_predictions;
+    cpu_predictor->PredictInstance(batch[i], &cpu_instance_out_predictions,
+                                   model);
+    gpu_predictor->PredictInstance(batch[i], &gpu_instance_out_predictions,
+                                   model);
+    ASSERT_EQ(gpu_instance_out_predictions[0], cpu_instance_out_predictions[0]);
+  }
+
+  // Test predict leaf
+  std::vector<float> gpu_leaf_out_predictions;
+  std::vector<float> cpu_leaf_out_predictions;
+  cpu_predictor->PredictLeaf(dmat.get(), &cpu_leaf_out_predictions, model);
+  gpu_predictor->PredictLeaf(dmat.get(), &gpu_leaf_out_predictions, model);
+  for (int i = 0; i < gpu_leaf_out_predictions.size(); i++) {
+    ASSERT_EQ(gpu_leaf_out_predictions[i], cpu_leaf_out_predictions[i]);
+  }
+
+  // Test predict contribution
+  std::vector<float> gpu_out_contribution;
+  std::vector<float> cpu_out_contribution;
+  cpu_predictor->PredictContribution(dmat.get(), &cpu_out_contribution, model);
+  gpu_predictor->PredictContribution(dmat.get(), &gpu_out_contribution, model);
+  for (int i = 0; i < gpu_out_contribution.size(); i++) {
+    ASSERT_EQ(gpu_out_contribution[i], cpu_out_contribution[i]);
+  }
+}
+}  // namespace predictor
+}  // namespace xgboost