third-party/benchmark/test/donotoptimize_test.cc

   1 #include <cstdint>
   2
   3 #include "benchmark/benchmark.h"
   4
   5 namespace {
   6 #if defined(__GNUC__)
   7 std::uint64_t double_up(const std::uint64_t x) __attribute__((const));
   8 #endif
   9 std::uint64_t double_up(const std::uint64_t x) { return x * 2; }
  10 }  // namespace
  11
  12 // Using DoNotOptimize on types like BitRef seem to cause a lot of problems
  13 // with the inline assembly on both GCC and Clang.
  14 struct BitRef {
  15   int index;
  16   unsigned char& byte;
  17
  18  public:
  19   static BitRef Make() {
  20     static unsigned char arr[2] = {};
  21     BitRef b(1, arr[0]);
  22     return b;
  23   }
  24
  25  private:
  26   BitRef(int i, unsigned char& b) : index(i), byte(b) {}
  27 };
  28
  29 int main(int, char*[]) {
  30   // this test verifies compilation of DoNotOptimize() for some types
  31
  32   char buffer8[8] = "";
  33   benchmark::DoNotOptimize(buffer8);
  34
  35   char buffer20[20] = "";
  36   benchmark::DoNotOptimize(buffer20);
  37
  38   char buffer1024[1024] = "";
  39   benchmark::DoNotOptimize(buffer1024);
  40   benchmark::DoNotOptimize(&buffer1024[0]);
  41
  42   int x = 123;
  43   benchmark::DoNotOptimize(x);
  44   benchmark::DoNotOptimize(&x);
  45   benchmark::DoNotOptimize(x += 42);
  46
  47   benchmark::DoNotOptimize(double_up(x));
  48
  49   // These tests are to e
  50   benchmark::DoNotOptimize(BitRef::Make());
  51   BitRef lval = BitRef::Make();
  52   benchmark::DoNotOptimize(lval);
  53 }