[hist] Add microbenchmarks for RAxes::ComputeGlobalIndex

This method will be extensively used during histogram filling, so it
should be fast.

Author: hahnjo

hist/histv7/benchmark/CMakeLists.txt

@@ -1,2 +1,5 @@
+add_executable(hist_benchmark_axes hist_benchmark_axes.cxx)
+target_link_libraries(hist_benchmark_axes ROOTHist benchmark::benchmark)
+
 add_executable(hist_benchmark_regular hist_benchmark_regular.cxx)
 target_link_libraries(hist_benchmark_regular ROOTHist benchmark::benchmark)

hist/histv7/benchmark/hist_benchmark_axes.cxx

@@ -0,0 +1,69 @@
+#include <ROOT/RAxes.hxx>
+
+#include <benchmark/benchmark.h>
+
+#include <random>
+#include <tuple>
+#include <vector>
+
+struct RAxes_Regular1 : public benchmark::Fixture {
+   // The objects are stored and constructed in the fixture to avoid compiler optimizations in the benchmark body taking
+   // advantage of the (constant) constructor parameters.
+   ROOT::Experimental::RRegularAxis axis{20, 0.0, 1.0};
+   ROOT::Experimental::Internal::RAxes axes{{axis}};
+   std::vector<double> fNumbers;
+
+   // Avoid GCC warning
+   using benchmark::Fixture::SetUp;
+   void SetUp(benchmark::State &state) final
+   {
+      std::mt19937 gen;
+      std::uniform_real_distribution<> dis;
+      fNumbers.resize(state.range(0));
+      for (std::size_t i = 0; i < fNumbers.size(); i++) {
+         fNumbers[i] = dis(gen);
+      }
+   }
+};
+
+BENCHMARK_DEFINE_F(RAxes_Regular1, ComputeGlobalIndex)(benchmark::State &state)
+{
+   for (auto _ : state) {
+      for (double number : fNumbers) {
+         benchmark::DoNotOptimize(axes.ComputeGlobalIndex(std::make_tuple(number)));
+      }
+   }
+}
+BENCHMARK_REGISTER_F(RAxes_Regular1, ComputeGlobalIndex)->Range(0, 32768);
+
+struct RAxes_Regular2 : public benchmark::Fixture {
+   // The objects are stored and constructed in the fixture to avoid compiler optimizations in the benchmark body taking
+   // advantage of the (constant) constructor parameters.
+   ROOT::Experimental::RRegularAxis axis{20, 0.0, 1.0};
+   ROOT::Experimental::Internal::RAxes axes{{axis, axis}};
+   std::vector<double> fNumbers;
+
+   // Avoid GCC warning
+   using benchmark::Fixture::SetUp;
+   void SetUp(benchmark::State &state) final
+   {
+      std::mt19937 gen;
+      std::uniform_real_distribution<> dis;
+      fNumbers.resize(2 * state.range(0));
+      for (std::size_t i = 0; i < fNumbers.size(); i++) {
+         fNumbers[i] = dis(gen);
+      }
+   }
+};
+
+BENCHMARK_DEFINE_F(RAxes_Regular2, ComputeGlobalIndex)(benchmark::State &state)
+{
+   for (auto _ : state) {
+      for (std::size_t i = 0; i < fNumbers.size(); i += 2) {
+         benchmark::DoNotOptimize(axes.ComputeGlobalIndex(std::make_tuple(fNumbers[i], fNumbers[i + 1])));
+      }
+   }
+}
+BENCHMARK_REGISTER_F(RAxes_Regular2, ComputeGlobalIndex)->Range(0, 32768);
+
+BENCHMARK_MAIN();