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

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Message-Id: <E1D1023D-4F2D-4EF4-8E97-CC5685B57A19@dell.com>
Date:	Mon, 8 Nov 2010 06:47:59 -0500
From:	Paul Koning <paul_koning@...l.com>
To:	Richard Guenther <richard.guenther@...il.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	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 ?


On Nov 8, 2010, at 6:20 AM, Richard Guenther wrote:

> On Mon, Nov 8, 2010 at 12:20 PM, Andi Kleen <andi@...stfloor.org> 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.
> 
> Please provide a testcase, such asms can be optimized if the
> outputs are dead.

I don't know about 4.5, but I noticed that with 4.6 (trunk), testcasese like gcc.c-torture/compile/20000804-1.c optimize away the asm and all the operand generation except for -O0.

	paul

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