Fix compiler warnings. (#8059)

- Remove unused parameters.
- Avoid comparison of different signedness.

src/tree/gpu_hist/evaluate_splits.cu

@@ -402,7 +402,7 @@ void GPUHistEvaluator<GradientSumT>::EvaluateSplits(
 
 template <typename GradientSumT>
 GPUExpandEntry GPUHistEvaluator<GradientSumT>::EvaluateSingleSplit(
-    EvaluateSplitInputs input, EvaluateSplitSharedInputs shared_inputs, float weight) {
+    EvaluateSplitInputs input, EvaluateSplitSharedInputs shared_inputs) {
   dh::device_vector<EvaluateSplitInputs> inputs = std::vector<EvaluateSplitInputs>{input};
   dh::TemporaryArray<GPUExpandEntry> out_entries(1);
   this->EvaluateSplits({input.nidx}, input.feature_set.size(), dh::ToSpan(inputs), shared_inputs,

src/tree/gpu_hist/evaluate_splits.cuh

@@ -167,19 +167,20 @@ class GPUHistEvaluator {
       TreeEvaluator::SplitEvaluator<GPUTrainingParam> evaluator);
 
   // impl of evaluate splits, contains CUDA kernels so it's public
-  void LaunchEvaluateSplits(bst_feature_t number_active_features,common::Span<const EvaluateSplitInputs> d_inputs,EvaluateSplitSharedInputs shared_inputs, 
+  void LaunchEvaluateSplits(bst_feature_t number_active_features,common::Span<const EvaluateSplitInputs> d_inputs,EvaluateSplitSharedInputs shared_inputs,
                       TreeEvaluator::SplitEvaluator<GPUTrainingParam> evaluator,
                       common::Span<DeviceSplitCandidate> out_splits);
   /**
    * \brief Evaluate splits for left and right nodes.
    */
   void EvaluateSplits(const std::vector<bst_node_t> &nidx,bst_feature_t number_active_features,common::Span<const EvaluateSplitInputs> d_inputs,
-                      EvaluateSplitSharedInputs shared_inputs, 
+                      EvaluateSplitSharedInputs shared_inputs,
                       common::Span<GPUExpandEntry> out_splits);
   /**
    * \brief Evaluate splits for root node.
    */
-  GPUExpandEntry EvaluateSingleSplit(EvaluateSplitInputs input,EvaluateSplitSharedInputs shared_inputs, float weight);
+  GPUExpandEntry EvaluateSingleSplit(EvaluateSplitInputs input,
+                                     EvaluateSplitSharedInputs shared_inputs);
 };
 }  // namespace tree
 }  // namespace xgboost

src/tree/gpu_hist/row_partitioner.cuh

@@ -272,7 +272,7 @@ class RowPartitioner {
     dh::TemporaryArray<PerNodeData<OpDataT>> d_batch_info(nidx.size());
 
     std::size_t total_rows = 0;
-    for (int i = 0; i < nidx.size(); i++) {
+    for (size_t i = 0; i < nidx.size(); i++) {
       h_batch_info[i] = {ridx_segments_.at(nidx.at(i)).segment, op_data.at(i)};
       total_rows += ridx_segments_.at(nidx.at(i)).segment.Size();
     }
@@ -295,7 +295,7 @@ class RowPartitioner {
     dh::safe_cuda(cudaStreamSynchronize(stream_));
 
     // Update segments
-    for (int i = 0; i < nidx.size(); i++) {
+    for (size_t i = 0; i < nidx.size(); i++) {
       auto segment = ridx_segments_.at(nidx[i]).segment;
       auto left_count = h_counts[i];
       CHECK_LE(left_count, segment.Size());