linux-kernel - Re: [tip:locking/core 9/11] include/asm-generic/atomic-instrumented.h:288:24: sparse: cast truncates bits from constant value (100 becomes 0)

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Date:   Tue, 13 Mar 2018 19:08:06 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Luc Van Oostenryck <luc.vanoostenryck@...il.com>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>, linux-sparse@...r.kernel.org,
        Christopher Li <sparse@...isli.org>,
        kbuild test robot <fengguang.wu@...el.com>,
        kbuild-all@...org, LKML <linux-kernel@...r.kernel.org>,
        tipbuild@...or.com, Ingo Molnar <mingo@...nel.org>
Subject: Re: [tip:locking/core 9/11]
 include/asm-generic/atomic-instrumented.h:288:24: sparse: cast truncates
 bits from constant value (100 becomes 0)

On Tue, Mar 13, 2018 at 07:00:17PM +0100, Luc Van Oostenryck wrote:
> The issue here is that sparse has a whole class of warnings that are
> given very early (here at expansion of constant expressions), before
> eliminating code from branches that are never taken (which, surprise,
> need itself to have constant expressions already expanded).
> 
> It's often annoying like the case here.
> OTOH, I don't think it's always a bad thing. Sometimes we want to
> have warnings even from code we know will not be executed (in this
> config but maybe it will in another one).

Is that really a valid concern with all the automated randconfig
building going on today?