linux-kernel - Re: gcc 4.5.1 / as 2.20.51.0.11 miscompiling drivers/char/i8k.c ?

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Date:	Mon, 8 Nov 2010 13:20:01 +0100 (CET)
From:	Michael Matz <matz@...e.de>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Richard Guenther <richard.guenther@...il.com>,
	Andreas Schwab <schwab@...ux-m68k.org>, Jim <jim876@...all.nl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	gcc@....gnu.org
Subject: Re: gcc 4.5.1 / as 2.20.51.0.11 miscompiling drivers/char/i8k.c ?

Hi,

On Mon, 8 Nov 2010, Andi Kleen wrote:

> Richard Guenther <richard.guenther@...il.com> writes:
> 
> > On Mon, Nov 8, 2010 at 12:03 AM, Andi Kleen <andi@...stfloor.org> wrote:
> >> Andreas Schwab <schwab@...ux-m68k.org> writes:
> >>>
> >>> The asm fails to mention that it modifies *regs.
> >>
> >> It has a memory clobber, that should be enough, no?
> >
> > No.  A memory clobber does not cover automatic storage.
> 
> That's a separate problem.
> 
> > Btw, I can't see a testcase anywhere so I just assume Andreas got
> > it right as usual.
> 
> An asm with live inputs and outputs should never be optimized
> way. If 4.5.1 started doing that it's seriously broken.

You know the drill: testcase -> gcc.gnu.org/bugzilla/

(In particular up to now it's only speculation in some forum that the asm 
really is optimized away, which I agree would be a bug, or if it isn't 
merely that regs->eax isn't reloaded after the asm(), which would be 
caused by the problem Andreas mentioned)


Ciao,
Michael.
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