Create a copy of the sets vector in InsertMiss_Hot

The benchmark loop of the InsertMiss_Hot benchmark modifies the sets in the vector. Therefore, we need to make a copy. Otherwise, repeated calls to `InsertMiss_Hot` (e.g., if the `--benchmark_repetitions` flag is set to a value larger than 1) start with increasingly larger sets, and thus the runtime of the benchmark grows with each repetition.

PiperOrigin-RevId: 747418678
Change-Id: I3327d6bbd6b9cb148c45100985f21e6148c60ffd

Author: andreas-abel

fleetbench/swissmap/hot_swissmap_benchmark.cc

@@ -18,6 +18,7 @@
 #include <cstdint>
 #include <memory>
 #include <string>
+#include <type_traits>
 #include <utility>
 #include <vector>
 
@@ -50,8 +51,11 @@ void FindMiss_Hot(benchmark::State& state) {
   static constexpr size_t kOpsPerKey = 512;
 
   auto& sc = SetsCache<Set>::GetInstance();
-  auto& sets = sc.GetGeneratedSets(state.range(0), kMinTotalKeyCount,
-                                   static_cast<Density>(state.range(1)));
+  // If kLookup is false, we need to create a copy of the cached sets vector
+  // because the benchmark loop modifies it.
+  std::conditional_t<kLookup, std::vector<Set>&, std::vector<Set>> sets =
+      sc.GetGeneratedSets(state.range(0), kMinTotalKeyCount,
+                          static_cast<Density>(state.range(1)));
   const size_t keys_per_set = kMinTotalKeyCount / sets.size();
 
   while (state.KeepRunningBatch(sets.size() * keys_per_set * kOpsPerKey)) {