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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug rtl-optimization/109930] transform atomic exchange to
 unconditional store when old value is unused?
Date: Mon, 22 May 2023 15:31:48 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: changed
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: rtl-optimization
X-Bugzilla-Version: 13.1.1
X-Bugzilla-Keywords: missed-optimization
X-Bugzilla-Severity: enhancement
X-Bugzilla-Who: pinskia at gcc dot gnu.org
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D109930

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 =3D x.exchange(5);
  (void)old_value;
}

void f0()
{
   x =3D 5;
}
```

Note on x86_64, these produce the same code generation anyways.
Though on aarch64, it does produce different code.=20

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