linux-kernel - Re: [RFC PATCH] LKMM: Add ctrl_dep() macro for control dependency

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Message-ID: <20211002142933.GA532982@rowland.harvard.edu>
Date:   Sat, 2 Oct 2021 10:29:33 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     Segher Boessenkool <segher@...nel.crashing.org>
Cc:     "Paul E. McKenney" <paulmck@...nel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        will@...nel.org, Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        parri.andrea@...il.com, boqun.feng@...il.com, npiggin@...il.com,
        dhowells@...hat.com, j.alglave@....ac.uk, luc.maranget@...ia.fr,
        akiyks@...il.com, linux-toolchains@...r.kernel.org,
        linux-arch@...r.kernel.org
Subject: Re: [RFC PATCH] LKMM: Add ctrl_dep() macro for control dependency

On Fri, Oct 01, 2021 at 02:10:08PM -0500, Segher Boessenkool wrote:
> Compilers understand you want exactly what you wrote.  If you write
> something other than what you want, you only will get what you want by
> pure luck.

The problem is that at times you _can't_ write what you want because the
language offers no way to express it.

Alan