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From: "wilco 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: Wed, 31 May 2023 17:29:45 +0000	[thread overview]
Message-ID: <bug-109930-4-eH3OYeBfeh@http.gcc.gnu.org/bugzilla/> (raw)
In-Reply-To: <bug-109930-4@http.gcc.gnu.org/bugzilla/>

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

Wilco <wilco at gcc dot gnu.org> changed:

           What    |Removed                     |Added
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                 CC|                            |wilco at gcc dot gnu.org

--- Comment #4 from Wilco <wilco at gcc dot gnu.org> ---
(In reply to Simon Richter from comment #3)
> I was looking at ARMv7 initially.
> 
> If I understood the implementation correctly, this can be a generic
> optimization.

This optimization is only valid for release or relaxed semantics, otherwise you
remove the acquire semantics of the exchange (without proof this is 100% safe,
this will likely allow an illegal reordering).

Btw if you know the old state then there is presumably no concurrent access
here and so you don't need atomic, let alone sequential consistency.

  parent reply	other threads:[~2023-05-31 17:29 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-05-22 10:49 [Bug rtl-optimization/109930] New: " Simon.Richter at hogyros dot de
2023-05-22 12:38 ` [Bug rtl-optimization/109930] " rguenth at gcc dot gnu.org
2023-05-22 15:31 ` pinskia at gcc dot gnu.org
2023-05-22 17:55 ` Simon.Richter at hogyros dot de
2023-05-31 17:29 ` wilco at gcc dot gnu.org [this message]
2023-06-01  1:40 ` Simon.Richter at hogyros dot de

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