[libc++] Add test case for benchmarking vector copy

[hiraditya]

Summary

Reported in: https://github.com/llvm/llvm-project/issues/61987

Fix proposed in: https://reviews.llvm.org/D147741

[philnik]

Let's add the benchmark and the changes in the same patch. That way you don't have to search for the benchmark/code changes.

libcxx/benchmarks/vector_operations.bench.cpp

22

This number looks weirdly specific. Why did you choose it?

[hiraditya]

libcxx/benchmarks/vector_operations.bench.cpp

22

copied from the test below, that's all. If you have other suggestions I'm okay with that.

[hiraditya]

In D148850#4303319, @philnik wrote:

Let's add the benchmark and the changes in the same patch. That way you don't have to search for the benchmark/code changes.

ok i'll abandon this patch then.

[hiraditya]

Merged in: https://reviews.llvm.org/D147741

libcxx/benchmarks/ContainerBenchmarks.h

void BM_ConstructSize(benchmark::State& st, Container) {
   auto size = st.range(0);
   for (auto _ : st) {
     Container c(size);
     DoNotOptimizeData(c);
   }
 }
 
 template <class Container>
+__attribute__((noinline))
+int CopyContainer(Container v1) {
+    auto v = v1;
+    return 0;
+}
+
+template <class Container>
+void BM_CopyConstruct(benchmark::State& st, Container) {
+  auto size = st.range(0);
+  for (auto _ : st) {
+    Container c(size);
+    auto v = CopyContainer(c);
+    DoNotOptimizeData(v);
+  }
+}
+
+template <class Container>
 void BM_ConstructSizeValue(benchmark::State& st, Container, typename Container::value_type const& val) {
   const auto size = st.range(0);
   for (auto _ : st) {
     Container c(size, val);
     DoNotOptimizeData(c);
   }
 }
 

libcxx/benchmarks/vector_operations.bench.cpp

 using namespace ContainerBenchmarks;
 
 constexpr std::size_t TestNumInputs = 1024;
 
 BENCHMARK_CAPTURE(BM_ConstructSize,
     vector_byte,
     std::vector<unsigned char>{})->Arg(5140480);
 
+BENCHMARK_CAPTURE(BM_CopyConstruct,
+    vector_int,
+    std::vector<int>{})->Arg(5140480);
+
 BENCHMARK_CAPTURE(BM_ConstructSizeValue,
     vector_byte,
     std::vector<unsigned char>{}, 0)->Arg(5140480);
 
 BENCHMARK_CAPTURE(BM_ConstructIterIter,
   vector_char,
   std::vector<char>{},
   getRandomIntegerInputs<char>)->Arg(TestNumInputs);