[Bug rtl-optimization/109930] transform atomic exchange to unconditional store when old value is unused?

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109930

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Target|                            |!i*86-* & !x86_64-*
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2023-05-22
           Keywords|                            |missed-optimization
             Status|UNCONFIRMED                 |NEW
           Severity|normal                      |enhancement

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Testcase:
```
#include <atomic>

std::atomic<uint32_t> x;
void f()
{
  auto old_value = x.exchange(5);
  (void)old_value;
}

void f0()
{
   x = 5;
}
```

Note on x86_64, these produce the same code generation anyways.
Though on aarch64, it does produce different code. 

I have a suspicion this was reported against x86_64 originally thinking these
two might produce different code generation ...