linux-kernel - Re: [PATCH] trivial: the memset operation on a automatic array variable should be optimized out by data initialization

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Message-ID: <Pine.LNX.4.64.0706180623280.11972@localhost.localdomain>
Date:	Mon, 18 Jun 2007 06:25:17 -0400 (EDT)
From:	"Robert P. J. Day" <rpjday@...dspring.com>
To:	Denis Cheng <crquan@...il.com>
cc:	trivial@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] trivial: the memset operation on a automatic array
 variable should be optimized out by data initialization

On Mon, 18 Jun 2007, Denis Cheng wrote:

> From: Denis Cheng <crquan@...il.com>
>
> the explicit memset call could be optimized out by data initialization,
> thus all the fill working can be done by the compiler implicitly.
>
> Signed-off-by: Denis Cheng <crquan@...il.com>
>
> ---
> Is there some comments on this?
>
> --- arch/x86_64/mm/init.c.orig	2007-06-07 10:08:04.000000000 +0800
> +++ arch/x86_64/mm/init.c	2007-06-18 14:43:15.000000000 +0800
> @@ -406,8 +406,7 @@ void __cpuinit zap_low_mappings(int cpu)
>  #ifndef CONFIG_NUMA
>  void __init paging_init(void)
>  {
> -	unsigned long max_zone_pfns[MAX_NR_ZONES];
> -	memset(max_zone_pfns, 0, sizeof(max_zone_pfns));
> +	unsigned long max_zone_pfns[MAX_NR_ZONES] = { 0, };

the drawback i see to this is that it's *visually* misleading.  it
*appears* that what the programmer is trying to do is just initialize
the first element, not all of them -- regardless of the actual effect.

rday
-- 
========================================================================
Robert P. J. Day
Linux Consulting, Training and Annoying Kernel Pedantry
Waterloo, Ontario, CANADA

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