[libc++] Fix minor warnings in libcxx benchmarks

[ilvokhin]

Summary

llvm-project/libcxx/benchmarks/allocation.bench.cpp:80:16: warning: unused
variable 'End' [-Wunused-variable]
   80 |   void** const End = Pointers.data() + Pointers.size();
      |

End is used in assert later, but benchmarks usually built in release
mode, so this warning triggers every time.

llvm-project/libcxx/benchmarks/monotonic_buffer.bench.cpp:19:26:
warning: comparison of integers of different signs: 'size_t' (aka 'unsigned
long') and 'int64_t' (aka 'long long') [-Wsign-compare]
   19 |     for (size_t i = 0; i != state.range(); ++i) {
      |

Made variable i type int64_t instead of size_t.

[ilvokhin]

Fix formatting.

[Mordante]

Thanks for working on this! A few comments.

libcxx/benchmarks/allocation.bench.cpp

80

I prefer a [[maybe_unused]] attribute instead. That makes it easier to inspect the value in the debugger.

libcxx/benchmarks/monotonic_buffer.bench.cpp

19

I see we use size_t in other benchmarks too. Can you fix all of them?

[ilvokhin]

Comments addressed.

[ilvokhin]

libcxx/benchmarks/monotonic_buffer.bench.cpp

19

Sure, I don't mind fixing others as well, but I couldn't find any.

The problem is state.range() as it returns int64_t. I searched for other use cases in libcxx/benchmarks and they don't have such problem as they result used to directly initialize vector size.

[ilvokhin]

Friendly ping @Mordante.

[Mordante]

Sorry I missed the ping. LGTM!

[ilvokhin]

Thanks for review. I don't have commit access. Could you please land the patch in my behalf?

Dmitry Ilvokhin
[e-mail]

libcxx/benchmarks/allocation.bench.cpp

static void BM_DeallocateOnly(benchmark::State& st) {
   const size_t alloc_size = st.range(0);
   const auto NumAllocs    = st.max_iterations;
 
   std::vector<void*> Pointers(NumAllocs);
   for (auto& p : Pointers) {
     p = AllocWrapper::Allocate(alloc_size);
   }
 
-  void** Data      = Pointers.data();
-  void** const End = Pointers.data() + Pointers.size();
+  void** Data                       = Pointers.data();
+  [[maybe_unused]] void** const End = Pointers.data() + Pointers.size();
   while (st.KeepRunning()) {
     AllocWrapper::Deallocate(*Data, alloc_size);
     Data += 1;
   }
   assert(Data == End);
 }
 
 static int RegisterAllocBenchmarks() {

libcxx/benchmarks/monotonic_buffer.bench.cpp

 
 #include "benchmark/benchmark.h"
 
 static void bm_list(benchmark::State& state) {
   char buffer[16384];
   std::pmr::monotonic_buffer_resource resource(buffer, sizeof(buffer));
   for (auto _ : state) {
     std::pmr::list<int> l(&resource);
-    for (size_t i = 0; i != state.range(); ++i) {
+    for (int64_t i = 0; i != state.range(); ++i) {
       l.push_back(1);
       benchmark::DoNotOptimize(l);
     }
     resource.release();
   }
 }
 BENCHMARK(bm_list)->Range(1, 2048);
 
 BENCHMARK_MAIN();