linux-kernel - Re: [PATCH 0/1] Dead stores in maple-tree

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Date:   Thu, 27 Oct 2022 10:43:15 +0300
From:   Dan Carpenter <dan.carpenter@...cle.com>
To:     Liam Howlett <liam.howlett@...cle.com>
Cc:     Lukas Bulwahn <lukas.bulwahn@...il.com>,
        Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "maple-tree@...ts.infradead.org" <maple-tree@...ts.infradead.org>
Subject: Re: [PATCH 0/1] Dead stores in maple-tree

On Wed, Oct 26, 2022 at 02:23:19PM +0000, Liam Howlett wrote:
> * Lukas Bulwahn <lukas.bulwahn@...il.com> [221026 08:01]:
> > Dear maple-tree authors, dear Liam, dear Matthew,
> > 
> > there are some Dead Stores that clang-analyzer reports:
> > 
> > lib/maple_tree.c:2906:2: warning: Value stored to 'last' is never read [clang-analyzer-deadcode.DeadStores]
> > lib/maple_tree.c:2907:2: warning: Value stored to 'prev_min' is never read [clang-analyzer-deadcode.DeadStores]
> > 
> > I addressed these two cases, which were most obvious and clear to fix;
> > see patch of this one-element series.
> > 
> > Further, clang-analyzer reports more, which I did not address:
> > 
> > lib/maple_tree.c:332:2: warning: Value stored to 'node' is never read [clang-analyzer-deadcode.DeadStores]
> > lib/maple_tree.c:337:2: warning: Value stored to 'node' is never read [clang-analyzer-deadcode.DeadStores]
> > 
> > Unclear to me if the tool is wrong or right in its analysis here for the two functions above.
> 
> The tool is correct but these aren't going anywhere.  They are compiled
> out and are needed for the future.
> 

lib/maple_tree.c
   330  static inline void mte_set_full(const struct maple_enode *node)
   331  {
   332          node = (void *)((unsigned long)node & ~MAPLE_ENODE_NULL);
   333  }
   334  
   335  static inline void mte_clear_full(const struct maple_enode *node)
   336  {
   337          node = (void *)((unsigned long)node | MAPLE_ENODE_NULL);
   338  }

That code is really puzzling...  How far into the future before it starts
making sense?

regards,
dan carpenter