Fix compiler warnings. (#7974)

- Remove unused parameters. There are still many warnings that are not yet
addressed. Currently, the warnings in dmlc-core dominate the error log.
- Remove `distributed` parameter from metric.
- Fixes some warnings about signed comparison.

tests/cpp/common/test_device_helpers.cu

@@ -67,7 +67,7 @@ TEST(SegmentedUnique, Basic) {
   CHECK_EQ(n_uniques, 5);
 
   std::vector<float> values_sol{0.1f, 0.2f, 0.3f, 0.62448811531066895f, 0.4f};
-  for (auto i = 0 ; i < values_sol.size(); i ++) {
+  for (size_t i = 0 ; i < values_sol.size(); i ++) {
     ASSERT_EQ(d_vals_out[i], values_sol[i]);
   }
 
@@ -84,7 +84,7 @@ TEST(SegmentedUnique, Basic) {
       d_segs_out.data().get(), d_vals_out.data().get(),
       thrust::equal_to<float>{});
   ASSERT_EQ(n_uniques, values.size());
-  for (auto i = 0 ; i < values.size(); i ++) {
+  for (size_t i = 0 ; i < values.size(); i ++) {
     ASSERT_EQ(d_vals_out[i], values[i]);
   }
 }

tests/cpp/common/test_linalg.cc

@@ -315,10 +315,10 @@ TEST(Linalg, Popc) {
 TEST(Linalg, Stack) {
   Tensor<float, 3> l{{2, 3, 4}, kCpuId};
   ElementWiseTransformHost(l.View(kCpuId), omp_get_max_threads(),
-                           [=](size_t i, float v) { return i; });
+                           [=](size_t i, float) { return i; });
   Tensor<float, 3> r_0{{2, 3, 4}, kCpuId};
   ElementWiseTransformHost(r_0.View(kCpuId), omp_get_max_threads(),
-                           [=](size_t i, float v) { return i; });
+                           [=](size_t i, float) { return i; });
 
   Stack(&l, r_0);
 

tests/cpp/common/test_partition_builder.cc

@@ -50,8 +50,8 @@ TEST(PartitionBuilder, BasicTest) {
         right[i] = left_total + value_right++;
       }
 
-      builder.SetNLeftElems(nid, begin, end, n_left);
-      builder.SetNRightElems(nid, begin, end, n_right);
+      builder.SetNLeftElems(nid, begin, n_left);
+      builder.SetNRightElems(nid, begin, n_right);
     }
   }
   builder.CalculateRowOffsets();

tests/cpp/common/test_quantile.cc

@@ -77,7 +77,7 @@ void TestDistributedQuantile(size_t rows, size_t cols) {
   std::vector<float> hessian(rows, 1.0);
   auto hess = Span<float const>{hessian};
 
-  ContainerType<use_column> sketch_distributed(n_bins, m->Info(), column_size, false, hess,
+  ContainerType<use_column> sketch_distributed(n_bins, m->Info(), column_size, false,
                                                OmpGetNumThreads(0));
 
   if (use_column) {
@@ -98,7 +98,7 @@ void TestDistributedQuantile(size_t rows, size_t cols) {
   CHECK_EQ(rabit::GetWorldSize(), 1);
   std::for_each(column_size.begin(), column_size.end(), [=](auto& size) { size *= world; });
   m->Info().num_row_ = world * rows;
-  ContainerType<use_column> sketch_on_single_node(n_bins, m->Info(), column_size, false, hess,
+  ContainerType<use_column> sketch_on_single_node(n_bins, m->Info(), column_size, false,
                                                   OmpGetNumThreads(0));
   m->Info().num_row_ = rows;
 
@@ -190,7 +190,7 @@ TEST(Quantile, SameOnAllWorkers) {
 
   constexpr size_t kRows = 1000, kCols = 100;
   RunWithSeedsAndBins(
-      kRows, [=](int32_t seed, size_t n_bins, MetaInfo const &info) {
+      kRows, [=](int32_t seed, size_t n_bins, MetaInfo const&) {
         auto rank = rabit::GetRank();
         HostDeviceVector<float> storage;
         std::vector<FeatureType> ft(kCols);

tests/cpp/common/test_span.h

@@ -36,7 +36,7 @@ struct TestTestStatus {
   XGBOOST_DEVICE void operator()() {
     this->operator()(0);
   }
-  XGBOOST_DEVICE void operator()(int _idx) {
+  XGBOOST_DEVICE void operator()(size_t) {  // size_t for CUDA index
     SPAN_ASSERT_TRUE(false, status_);
   }
 };
@@ -49,7 +49,7 @@ struct TestAssignment {
   XGBOOST_DEVICE void operator()() {
     this->operator()(0);
   }
-  XGBOOST_DEVICE void operator()(int _idx) {
+  XGBOOST_DEVICE void operator()(size_t) {  // size_t for CUDA index
     Span<float> s1;
 
     float arr[] = {3, 4, 5};
@@ -71,7 +71,7 @@ struct TestBeginEnd {
   XGBOOST_DEVICE void operator()() {
     this->operator()(0);
   }
-  XGBOOST_DEVICE void operator()(int _idx) {
+  XGBOOST_DEVICE void operator()(size_t) {  // size_t for CUDA index
     float arr[16];
     InitializeRange(arr, arr + 16);
 
@@ -93,7 +93,7 @@ struct TestRBeginREnd {
   XGBOOST_DEVICE void operator()() {
     this->operator()(0);
   }
-  XGBOOST_DEVICE void operator()(int _idx) {
+  XGBOOST_DEVICE void operator()(size_t) {  // size_t for CUDA index
     float arr[16];
     InitializeRange(arr, arr + 16);
 
@@ -121,7 +121,7 @@ struct TestObservers {
   XGBOOST_DEVICE void operator()() {
     this->operator()(0);
   }
-  XGBOOST_DEVICE void operator()(int _idx) {
+  XGBOOST_DEVICE void operator()(size_t) {  // size_t for CUDA index
     // empty
     {
       float *arr = nullptr;
@@ -148,7 +148,7 @@ struct TestCompare {
   XGBOOST_DEVICE void operator()() {
     this->operator()(0);
   }
-  XGBOOST_DEVICE void operator()(int _idx) {
+  XGBOOST_DEVICE void operator()(size_t) {  // size_t for CUDA index
     float lhs_arr[16], rhs_arr[16];
     InitializeRange(lhs_arr, lhs_arr + 16);
     InitializeRange(rhs_arr, rhs_arr + 16);
@@ -178,7 +178,7 @@ struct TestIterConstruct {
   XGBOOST_DEVICE void operator()() {
     this->operator()(0);
   }
-  XGBOOST_DEVICE void operator()(int _idx) {
+  XGBOOST_DEVICE void operator()(size_t) {  // size_t for CUDA index.
     Span<float>::iterator it1;
     Span<float>::iterator it2;
     SPAN_ASSERT_TRUE(it1 == it2, status_);
@@ -197,7 +197,7 @@ struct TestIterRef {
   XGBOOST_DEVICE void operator()() {
     this->operator()(0);
   }
-  XGBOOST_DEVICE void operator()(int _idx) {
+  XGBOOST_DEVICE void operator()(size_t) {  // size_t for CUDA index
     float arr[16];
     InitializeRange(arr, arr + 16);
 
@@ -215,7 +215,7 @@ struct TestIterCalculate {
   XGBOOST_DEVICE void operator()() {
     this->operator()(0);
   }
-  XGBOOST_DEVICE void operator()(int _idx) {
+  XGBOOST_DEVICE void operator()(size_t) {  // size_t for CUDA index
     float arr[16];
     InitializeRange(arr, arr + 16);
 
@@ -278,7 +278,7 @@ struct TestAsBytes {
   XGBOOST_DEVICE void operator()() {
     this->operator()(0);
   }
-  XGBOOST_DEVICE void operator()(int _idx) {
+  XGBOOST_DEVICE void operator()(size_t) {  // size_t for CUDA index
     float arr[16];
     InitializeRange(arr, arr + 16);
 
@@ -313,7 +313,7 @@ struct TestAsWritableBytes {
   XGBOOST_DEVICE void operator()() {
     this->operator()(0);
   }
-  XGBOOST_DEVICE void operator()(int _idx) {
+  XGBOOST_DEVICE void operator()(size_t) {  // size_t for CUDA index
     float arr[16];
     InitializeRange(arr, arr + 16);
 

tests/cpp/common/test_threading_utils.cc

@@ -34,9 +34,8 @@ TEST(ParallelFor2d, Test) {
 
   // working space is matrix of size (kDim1 x kDim2)
   std::vector<int> matrix(kDim1 * kDim2, 0);
-  BlockedSpace2d space(kDim1, [&](size_t i) {
-      return kDim2;
-  }, kGrainSize);
+  BlockedSpace2d space(
+      kDim1, [&](size_t) { return kDim2; }, kGrainSize);
 
   auto old = omp_get_max_threads();
   omp_set_num_threads(4);