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Date: Thu, 25 May 2017 21:43:43 -0700
From: Nick Desaulniers <nick.desaulniers@gmail.com>
Subject: Re: [Patch v2] mm/vmscan: fix unsequenced modification and access
 warning
Message-ID: <20170526044343.autu63rpfigbzhyi@lostoracle.net>
References: <20170510071511.GA31466@dhcp22.suse.cz>
 <20170510082734.2055-1-nick.desaulniers@gmail.com>
 <20170510083844.GG31466@dhcp22.suse.cz>
 <20170516082746.GA2481@dhcp22.suse.cz>
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To: Michal Hocko <mhocko@kernel.org>
Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, mgorman@techsingularity.net, vbabka@suse.cz, minchan@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org

On Tue, May 16, 2017 at 10:27:46AM +0200, Michal Hocko wrote:
> I guess it is worth reporting this to clang bugzilla. Could you take
> care of that Nick?

>>From https://bugs.llvm.org//show_bug.cgi?id=33065#c5
it seems that this is indeed a sequence bug in the previous version of
this code and not a compiler bug.  You can read that response for the
properly-cited wording but my TL;DR/understanding is for the given code:

struct foo bar = {
  .a = (c = 0),
  .b = c,
};

That the compiler is allowed to reorder the initializations of bar.a and
bar.b, so what the value of c here might not be what you expect.

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