[Bug tree-optimization/66713] atomic compare_exchange_strong creates spurious store for x86-64 at -O3

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66713

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
#include <atomic>

float *ptr;
std::atomic<float*> aptr;

template <typename T> 
T cas_original (T cmp_, T val_) {
  T old;
  __asm volatile(
     "lock; cmpxchgq %2, %3"
     : "=a" (old), "=m" (ptr)
     : "r" (val_), "m" (ptr), "0" (cmp_)
     : "cc"
  );
  return old;
}

template <typename T>
T cas_atomic( T cmp_, T val_) {
  aptr.compare_exchange_strong(cmp_, val_, std::memory_order_acq_rel);
  return cmp_;
}

void driver_original(float *a, float *b) {
  cas_original(a, b);
}

void driver_atomic(float *a, float *b) {
  cas_atomic(a, b);
}