llvm-project/libcxx/utils/google-benchmark/test/donotoptimize_test.cc

#include "benchmark/benchmark.h"

#include <cstdint>

namespace {
#if defined(__GNUC__)
std::uint64_t double_up(const std::uint64_t x) __attribute__((const));
#endif
std::uint64_t double_up(const std::uint64_t x) { return x * 2; }
}

// Using DoNotOptimize on types like BitRef seem to cause a lot of problems
// with the inline assembly on both GCC and Clang.
struct BitRef {
  int index;
  unsigned char &byte;

public:
  static BitRef Make() {
    static unsigned char arr[2] = {};
    BitRef b(1, arr[0]);
    return b;
  }
private:
  BitRef(int i, unsigned char& b) : index(i), byte(b) {}
};

int main(int, char*[]) {
  // this test verifies compilation of DoNotOptimize() for some types

  char buffer8[8] = "";
  benchmark::DoNotOptimize(buffer8);

  char buffer20[20] = "";
  benchmark::DoNotOptimize(buffer20);

  char buffer1024[1024] = "";
  benchmark::DoNotOptimize(buffer1024);
  benchmark::DoNotOptimize(&buffer1024[0]);

  int x = 123;
  benchmark::DoNotOptimize(x);
  benchmark::DoNotOptimize(&x);
  benchmark::DoNotOptimize(x += 42);

  benchmark::DoNotOptimize(double_up(x));

  // These tests are to e
  benchmark::DoNotOptimize(BitRef::Make());
  BitRef lval = BitRef::Make();
  benchmark::DoNotOptimize(lval);
}