https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93648
--- Comment #7 from Roman Zhikharevich <rzhikharev...@yandex-team.ru> ---
I am writing benchmarking code for my project and trying to make the compiler
ignore its knowledge of certain values during optimization. I settled for
template <typename T>
void black_box(T* value) {
asm volatile ("" :: "g"(value) : "memory");
}
but I am trying to figure out the reasoning behind Google Benchmark's
implementation of similar functionality:
https://github.com/google/benchmark/blob/7d97a057e16597e8020d0aca110480fe82c9ca67/include/benchmark/benchmark.h#L318
They use
template <class Tp>
inline BENCHMARK_ALWAYS_INLINE void DoNotOptimize(Tp& value) {
#if defined(__clang__)
asm volatile("" : "+r,m"(value) : : "memory");
#else
asm volatile("" : "+m,r"(value) : : "memory");
#endif
}
