linux-kernel - Re: gcc inlining heuristics was Re: [PATCH -v7][RFC]: mutex: implement adaptive spinning

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Date:	Mon, 12 Jan 2009 12:11:07 -0800 (PST)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Bernd Schmidt <bernds_cb1@...nline.de>
cc:	Andi Kleen <andi@...stfloor.org>,
	David Woodhouse <dwmw2@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Harvey Harrison <harvey.harrison@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Chris Mason <chris.mason@...cle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	paulmck@...ux.vnet.ibm.com, Gregory Haskins <ghaskins@...ell.com>,
	Matthew Wilcox <matthew@....cx>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-btrfs <linux-btrfs@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Nick Piggin <npiggin@...e.de>,
	Peter Morreale <pmorreale@...ell.com>,
	Sven Dietrich <SDietrich@...ell.com>, jh@...e.cz
Subject: Re: gcc inlining heuristics was Re: [PATCH -v7][RFC]: mutex: implement
 adaptive spinning



On Mon, 12 Jan 2009, Bernd Schmidt wrote:
> 
> However, if the compiler chooses to put them into the same stack 
> location, the RTL-based alias analysis will happily conclude (based on 
> the differing types) that the reads from A and the writes to B can't 
> possibly conflict, and some passes may end up reordering them. End 
> result: overlapping lifetimes and overlapping stack slots.  Oops.

Yes, I came to the same conclusion.

Of course, I knew a-priori that the real bug was using type-based alais 
analysis to make (statically visible) aliasing decisions, but I realize 
that there are people who never understood things like that. Sadly, some 
of them worked on gcc.

			Linus
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