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: <20070623135721.GP23017@stusta.de>
Date:	Sat, 23 Jun 2007 15:57:21 +0200
From:	Adrian Bunk <bunk@...sta.de>
To:	Oleg Verych <olecom@...wer.upol.cz>
Cc:	Denis Cheng <crquan@...il.com>, 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 Sat, Jun 23, 2007 at 03:41:26PM +0200, Oleg Verych wrote:
> On Sat, Jun 23, 2007 at 03:13:55PM +0200, Adrian Bunk wrote:
> > On Sat, Jun 23, 2007 at 09:59:33AM +0200, Oleg Verych 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.
> > > 
> > > Can be optimized and can be done by compiler are just words;
> > > 
> > > > and C standard guaranteed all the unspecified data field initialized to zero.
> > > 
> > > standards and implementation are on opposite poles of magnet
> > 
> > Bullshit.
> > 
> > We expect a C compiler, and if a C compiler violates the C standard 
> > that's a bug in the compiler that has to be fixed.
> 
> If you are serious, please consider last kernel headers vs ANSI C
> discussion,

If only Joerg would tell us where the problem exactly is...

There might be a bug in the kernel header, but this simply has to be 
fixed.

> then GNU extensions of the GCC C compiler and relevant "if
> ICC doesn't support GCC extensions it's ICC's bug".

gcc is a C compiler and claims to follow the C standard.
The kernel does not claim to be compilable by a plain C compiler.

Spot the difference?

> That was about
> implementation. About standards you are not serious, aren't you?
> (Please don't see this as for this particular case, but as general
> viewpoint)

And as with many generalizations, that's often wrong...

> > And gcc is usually quite good in following the C standard.
> 
> > > > Signed-off-by: Denis Cheng <crquan@...il.com>
> > > >
> > > > ---
> > > > After comments in the former threads:
> > > > http://lkml.org/lkml/2007/6/18/119
> > > 
> > > i see a patch
> > > 
> > > > http://lkml.org/lkml/2007/6/18/48
> > > 
> > > same patch.
> > >...
> > 
> > Open your eyes and you'll find thread overviews at the left side of 
> > the URLs he gave...
> 
> Two threads with *different* URLs but with *same* patch...
>...

The comments are in the _threads_.
The patches are only the roots of the threads.

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

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