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

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Message-ID: <20101115224645.GI29412@tyan-ft48-01.lab.bos.redhat.com>
Date:	Mon, 15 Nov 2010 23:46:45 +0100
From:	Jakub Jelinek <jakub@...hat.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Jim Bos <jim876@...all.nl>, James Cloos <cloos@...loos.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andreas Schwab <schwab@...hat.com>,
	Michael Matz <matz@...e.de>,
	Dave Korn <dave.korn.cygwin@...il.com>,
	Richard Guenther <richard.guenther@...il.com>, gcc@....gnu.org
Subject: Re: gcc 4.5.1 / as 2.20.51.0.11 miscompiling drivers/char/i8k.c ?

On Mon, Nov 15, 2010 at 11:43:22PM +0100, Andi Kleen wrote:
> > testcase shows that in 4.1/4.2/4.3/4.4 this is miscompiled only when using
> > -fno-ipa-reference, in 4.5 it is miscompiled always when optimizing
> > unless -fno-ipa-pure-const (as 4.5 added local-pure-const pass which is run
> > before ipa-reference) and in 4.6 this has been fixed by Honza when
> > doing ipa cleanups.
> 
> Maybe it would be better to simply change the kernel Makefiles to pass
> -fno-ipa-pure-const instead of adding volatiles everywhere.

If you do this, please do it for 4.5.[012] only.  If you disable all gcc
passes that ever had any bugs in it, you'd need to disable most of them if
not all.

	Jakub
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