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

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Message-ID: <20101115100331.GG2583@sunsite.ms.mff.cuni.cz>
Date:	Mon, 15 Nov 2010 11:03:32 +0100
From:	Jakub Jelinek <jakub@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	James Cloos <cloos@...loos.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andreas Schwab <schwab@...hat.com>,
	Andi Kleen <andi@...stfloor.org>, Michael Matz <matz@...e.de>,
	Dave Korn <dave.korn.cygwin@...il.com>,
	Richard Guenther <richard.guenther@...il.com>, gcc@....gnu.org,
	Jim Bos <jim876@...all.nl>
Subject: Re: gcc 4.5.1 / as 2.20.51.0.11 miscompiling drivers/char/i8k.c ?

On Mon, Nov 15, 2010 at 09:56:05AM +0100, Jakub Jelinek wrote:
> On Sun, Nov 14, 2010 at 07:21:50PM -0800, Linus Torvalds wrote:
> > So when Richard Gunther says "a memory clobber doesn't cover automatic
> > storage", to me that very clearly spells "gcc is buggy as hell".
> > Because automatic storage with its address taken _very_ much gets
> > clobbered by things like memset etc. If the compiler doesn't
> > understand that, the compiler is just broken.
> 
> I'll leave the discussion about meaning of "memory" clobber aside to
> Richard,

And for this the starting point should be what has been requested,
i.e. preprocessed source + gcc options + gcc version and some hints what
actually misbehaves (with the , "+m" (*regs) change reverted)
in gcc bugzilla.  Only with that we can actually look at what has been
happening, see whether it is the tree optimizations or RTL and which one
makes a difference.
If I've missed a PR about this I apologize. 

	Jakub
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