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Date:   Wed, 5 Jul 2023 00:05:32 -0700
From:   Boqun Feng <boqun.feng@gmail.com>
To:     Olivier Dion <odion@efficios.com>
Cc:     Mathieu Desnoyers <mathieu.desnoyers@efficios.com>, rnk@google.com,
        Alan Stern <stern@rowland.harvard.edu>,
        Andrea Parri <parri.andrea@gmail.com>,
        Will Deacon <will@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Nicholas Piggin <npiggin@gmail.com>,
        David Howells <dhowells@redhat.com>,
        Jade Alglave <j.alglave@ucl.ac.uk>,
        Luc Maranget <luc.maranget@inria.fr>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Tom Rix <trix@redhat.com>, linux-kernel@vger.kernel.org,
        linux-arch@vger.kernel.org, gcc@gcc.gnu.org, llvm@lists.linux.dev
Subject: Re: [RFC] Bridging the gap between the Linux Kernel Memory
 Consistency Model (LKMM) and C11/C++11 atomics
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On Mon, Jul 03, 2023 at 03:20:31PM -0400, Olivier Dion wrote:
[...]
> NOTE: On x86-64, we found at least one corner case [7] with Clang where
> a RELEASE exchange is optimized to a RELEASE store, when the returned
> value of the exchange is unused, breaking the above expectations.
> Although this type of optimization respect the standard "as-if"
> statement, we question its pertinence since a user should simply do a
> RELEASE store instead of an exchange in that case.  With the
> introduction of these new primitives, these type of optimizations should
> be revisited.
> 

FWIW, this is actually a LLVM bug:

	https://github.com/llvm/llvm-project/issues/60418

Regards,
Boqun