Add increment benchmark as baseline

Author: jerryct

core/benchmarks/counter_bench.cc

@@ -1,6 +1,19 @@
 #include <benchmark/benchmark.h>
 #include <prometheus/registry.h>
 
+static void BM_Counter_IncrementBaseline(benchmark::State& state) {
+  struct {
+    void Increment() { v += 1.0; }
+    double v;
+  } counter;
+
+  for (auto _ : state) {
+    counter.Increment();
+  }
+  benchmark::DoNotOptimize(counter.v);
+}
+BENCHMARK(BM_Counter_IncrementBaseline);
+
 static void BM_Counter_Increment(benchmark::State& state) {
   using prometheus::BuildCounter;
   using prometheus::Counter;
@@ -10,9 +23,10 @@ static void BM_Counter_Increment(benchmark::State& state) {
       BuildCounter().Name("benchmark_counter").Help("").Register(registry);
   auto& counter = counter_family.Add({});
 
-  while (state.KeepRunning()) {
+  for (auto _ : state) {
     counter.Increment();
   }
+  benchmark::DoNotOptimize(counter.Value());
 }
 BENCHMARK(BM_Counter_Increment);
 
@@ -28,6 +42,7 @@ BENCHMARK_F(BM_Counter, ConcurrentIncrement)
   for (auto _ : state) {
     counter.Increment();
   }
+  benchmark::DoNotOptimize(counter.Value());
 }
 
 static void BM_Counter_Collect(benchmark::State& state) {