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From: "pinskia at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug tree-optimization/111739] incorrect code with PGO enabled
Date: Thu, 19 Oct 2023 01:37:56 +0000	[thread overview]
Message-ID: <bug-111739-4-j35Hn1uWRC@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-111739-4@http.gcc.gnu.org/bugzilla/>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111739

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |INVALID

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The code is undefined for alias reasons:
union {
  int f;
  short g
} h;
*j = &h;

...
  a = n(h.f++);
  *j = 0;
...
  for (; i < 2; i++)
    d = k(h.g || 0, 59376);
  short *b = &h;
  *b ^= e;
  printf("%d\n", h);
```

In the case of profiling, we are able to optimize away the short load from h
in:
  *b ^= e;
and point it back to the store from `h.f++` and miss the store via *j.

Once you add -fno-strict-aliasing the testcase starts to work.

      parent reply	other threads:[~2023-10-19  1:37 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-10-09 12:50 [Bug tree-optimization/111739] New: " iamanonymous.cs at gmail dot com
2023-10-09 13:17 ` [Bug tree-optimization/111739] " rguenth at gcc dot gnu.org
2023-10-09 13:34 ` iamanonymous.cs at gmail dot com
2023-10-19  1:37 ` pinskia at gcc dot gnu.org [this message]

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