C++14 for xgboost (#5664)

src/CMakeLists.txt

@@ -14,7 +14,6 @@ if (USE_CUDA)
     $<$<COMPILE_LANGUAGE:CUDA>:--expt-extended-lambda>
     $<$<COMPILE_LANGUAGE:CUDA>:--expt-relaxed-constexpr>
     $<$<COMPILE_LANGUAGE:CUDA>:-lineinfo>
-    $<$<AND:$<NOT:$<CXX_COMPILER_ID:MSVC>>,$<COMPILE_LANGUAGE:CUDA>>:--std=c++11>
     $<$<COMPILE_LANGUAGE:CUDA>:${GEN_CODE}>)
 
   if (USE_NCCL)
@@ -45,6 +44,8 @@ if (USE_CUDA)
   endif (HIDE_CXX_SYMBOLS)
 
   set_target_properties(objxgboost PROPERTIES
+    CUDA_STANDARD 14
+    CUDA_STANDARD_REQUIRED ON
     CUDA_SEPARABLE_COMPILATION OFF)
 else (USE_CUDA)
   add_library(objxgboost OBJECT ${CPU_SOURCES} ${PLUGINS_SOURCES})
@@ -71,7 +72,7 @@ endif (MSVC)
 
 set_target_properties(objxgboost PROPERTIES
   POSITION_INDEPENDENT_CODE ON
-  CXX_STANDARD 11
+  CXX_STANDARD 14
   CXX_STANDARD_REQUIRED ON)
 target_compile_definitions(objxgboost
   PRIVATE

src/common/column_matrix.h

@@ -35,6 +35,8 @@ class Column {
         index_(index),
         index_base_(index_base) {}
 
+  virtual ~Column() = default;
+
   uint32_t GetGlobalBinIdx(size_t idx) const {
     return index_base_ + static_cast<uint32_t>(index_[idx]);
   }

src/objective/rank_obj.cu

@@ -314,7 +314,7 @@ class NDCGLambdaWeightComputer
       for (size_t i = 0; i < sorted_list.size(); ++i) {
         labels[i] = sorted_list[i].label;
       }
-      std::stable_sort(labels.begin(), labels.end(), std::greater<bst_float>());
+      std::stable_sort(labels.begin(), labels.end(), std::greater<>());
       IDCG = ComputeGroupDCGWeight(&labels[0], labels.size());
     }
     if (IDCG == 0.0) {

src/tree/updater_histmaker.cc

@@ -699,7 +699,7 @@ class GlobalProposalHistMaker: public CQHistMaker {
       this->work_set_.insert(this->work_set_.end(), this->fsplit_set_.begin(),
                              this->fsplit_set_.end());
       XGBOOST_PARALLEL_SORT(this->work_set_.begin(), this->work_set_.end(),
-                            std::less<decltype(this->work_set_)::value_type>{});
+                            std::less<>{});
       this->work_set_.resize(
           std::unique(this->work_set_.begin(), this->work_set_.end()) - this->work_set_.begin());